# McKinsey PST: A comprehensive guide

The McKinsey Problem Solving Test (McKinsey PST) is a data interpretation and critical number reasoning test used by McKinsey to select candidates to be admitted to the first round of case interviews.

## All you need to know about the McKinsey Problem Solving Test in 6 facts

1. 26 questions, paper and pen

The McKinsey PST is a multiple choice paper test made up of 26 questions distributed over three business cases. The cases test how you would perform in the different phases of a consulting project: client interaction, problem definition, problem solving, analytical work and implementation. Topics are the same as in real consulting projects, ranging from market entry to profitability or operational improvements.

2. 60 minutes

Simply put: if you had 3 hours to complete the test, you would easily score over 80%. Time is the real, big constraint of the PST. And since you will not be able to use any other device besides your brain, it is essential for you to develop the best skill set and test the most effective method.

3. Make it or break it

No matter how outstanding your resume is, if you fail the McKinsey PST, you will not be invited to the first round of interviews. If you pass the PST, McKinsey will use your PST score together with feedback from your interviewers to decide if you should be given an offer or not.

4. 70% cutoff score

While McKinsey does not publish the exact cut-off score for its Problem Solving Test, it is estimated to be around 70%. Estimates are based on interviews and surveys to successful candidates. Succeeding at the test depends only on YOUR score: scoring is absolute, not relative. Bear in mind to always answer all questions, as there is no penalization for wrong answers.

5. 1 out of 3 makes it

Although scoring is not on a curve, unofficial surveys tell us that about 1 out of 3 candidates passes the test and progresses to the interview round. The PST is the big differentiator in the recruiting process between McKinsey and its main competitors.

6. Not the GMAT

Although scoring is not on a curve, unofficial surveys tell us that about 1 out of 3 candidates passes the test and progresses to the interview round. The PST is the big differentiator in the recruiting process between McKinsey and its main competitors.

## What kind of questions will you get in the PST?

The test consists of three business cases with 8-10 questions each, ideally replicating a consulting engagement. As in a real project, in every business case you will be presented with data in charts or tables as well as descriptive text. Usually, every piece of information is followed by 2-3 questions that refer specifically to the information provided.
Questions can be broken down in 6 types in the PST. These are:

### Reading facts (~35% OF THE PST)

Reading facts questions will test your ability to extract and elaborate data from graphs and table. They are the most common question type, constituting ~35% of the test.
Some examples:

Which of the following values is the best estimate of ABC revenue in Year 4?
To the nearest tenth percentage point, what is the difference between Italy’s and Spain’s respective average annual agriculture sector growths due to fertilizing over the last 10 years?

#### What is it?

This is the most common question type in the McKinsey PST (~35%). You will be tested on your ability to understand the facts/data itself, often in the form of graphs and tables.

#### Question Formats

• Which of the following values is the best estimate of ...?
• Which of the following statements is valid, based on the data ...?
• What is the current ranking of options 1 to 5?

#### Example

The table below shows the sales development of the Topstar business unit across the main markets.

US$M 2008 2009 2010 2011 2012 US 240 282 343 405 469 Germany 144 165 186 204 237 Italy 45 58 58 75 82 China 60 69 67 71 74 Japan 58 50 50 56 58 Which of these markets showed the fastest sales development (in %-terms) from 2009-2012? 1. US 2. Germany 3. Italy 4. Japan #### Method 1. Read the question - pretty straightforward, as you are asked to identify the country with the highest growth rate. 2. Read the answers - there are 4 countries to be compared. 3. Go back to the table and compare the growth rate between 2009 and 2012 only in those 4 countries. Simplify figures as much as possible and run precise calculations only if you find out that the difference between two countries is not high enough to guarantee a reliable result through simplification. 4. Now, you need to first define the calculation you need to solve in order to get market growth, which will be: $\frac{\text{Sales}\textsubscript{2012}\ -\ \text{Sales}\textsubscript{2009}}{\text{Sales}\textsubscript{2009}}$ Then start with the first option (the US). Approximately, the growth in the US will be $\frac{470-280}{280} = \frac{190}{280}$, which is much higher than 50%, as it is around 70%. Move on to other countries, comparing them solely with the US. Germany will be approximately $\frac{240-165}{165} = \frac{85}{165}$, very close to 50%. Cross out Germany. Moving on to Italy, the calculation will be $\frac{80-60}{60} = \frac{20}{60}$, which is lower than 50% again. Cross out Italy. In Japan, the growth was from 50 to 58, therefore there is no need for lengthy calculations to cross it out. This leaves the US (answer A) as the right answer. #### Tips & Tricks • Begin with an end in mind. Before performing any calculations, be clear on which formula/equation you need to use. In the PST there is not much time for trial and error. Spending just a few more seconds on identifying the right formula to use from the very beginning will save you much more precious time in the calculation phase. • Minimize the number of calculations. When going through your solutions, you will be surprised by how many calculations can be avoided or approximated mentally. The key question you should ask yourself before performing any calculation is: does it affect the answer? It might sound silly, but it is definitely relevant and useful. Here are just two of the most useful techniques to avoid useless calculations: • The anchoring technique. When looking for the highest value among several possible answers, run calculations for the first answer and use that value as a threshold value. If other answers look immediately lower, do not perform any further calculations. • The selection technique. Select the only the essential calculations. For example, the question below asks you to rank the effectiveness of 5 solutions: 1. 1, 2, 4, 3, 5 2. 1, 2, 3, 4, 5 3. 1, 3, 2, 4, 5 4. 1, 3, 2, 5, 4 Calculating whether solution A is the most effective is a complete waste of your time — it is the least answer-changing analysis. Then go on calculating which is the most effective between solution B and C. And so on and so forth. • Master quick percentage calculations. Growth rates and percentages are extremely common across the PST. You will surely encounter questions in which you’ll have to calculate growth rates over multiple time periods. This is theoretically feasible by hand, but extremely time-consuming. If, for example, the revenues of a given company are growing at a 5% per year rate for 4 years, in order to get a precise result, you'd need to calculate the four years compounded growth rate: $(1 + 0.05) * (1 + 0.05) * (1 + 0.05) = 1.27 = 21% growth over 4-year period$ You cannot afford going through such a time consuming process in the PST. It would likely take you more than two minutes and you will not have time for completing the answer to your question (usually the PST asks you for much more than calculating percentages). You will be able to solve this kind of problem by using the following simple shortcut. Multiply the yearly growth rate by the number of years during which it will apply and you will get an estimate of the compounded growth rate: $\text{5\% per year}\ *\ \text{4 years} = \text{20\% growth over 4 years}$ There are few caveats to bear in mind when using this technique: • When using positive growth rates, the growth rate will be underestimated. The above estimation is 20% vs. 21% growth from the real figure. When using negative growth rates, it will overestimate the compounded growth rate. • The higher the yearly growth rate and the number of years to which you are applying the technique, the less precise it becomes. For instance, 5 years of growth at 5% per year corresponds to a 27% compounded growth rate while our shortcut would give us a compounded growth of 25% (5% per year x 5 years). ### Root-cause reasons (~18% OF THE PST) Which of the following, if true, LEAST explains the data for Slovenia and the Czech Republic in Exhibit 2? Root cause reason questions test your ability to identify the underlying causes of a business problem. You can also find a video on our course. Some examples are: Which of the following reasons, if TRUE, is most likely to be the reason for the drop in house prices in year 2? #### What is it? The root cause reason question type asks candidates to select from among the proposed answers the one that may actually constitute the reason behind the fact stated in the question. #### Question Formats • Which of the following reasons, if TRUE, best explains the reason why the CEO wants to proceed to cost reduction? • Which of the following does NOT help to explain why ...? • Which of the following, if TRUE, would best challenge the sales manager's decision? #### Example Zapclothing is a global fast fashion retailer catering to teenage girls, which owns shops all over Europe. Five years ago, the top management of Zapclothing decided to embark on an upmarket move, in order to cater to a slightly older and more affluent customer base. Leading Italian and French stylists were hired by Zapclothing to create bespoke and unique clothing designs. Prices were raised on the whole product line by 20%-30% and a series of events in all major global cities was launched in order to build a more upscale and sophisticated brand image. Whilst initially the mid-market transition boosted profit margins without altering sales volumes, one year after the introduction of upscale clothing the company found itself with plummeting revenues and a decreasing profit margin. In order to bring back profit volumes to the previous higher levels, the marketing manager proposed a permanent price reduction of 10% across the board on all product lines. Which of the following facts, if true, would best challenge the sales manager’s proposal for price reduction? 1. Over the last year, due to higher commodity costs, prices increased on average by 15% for the whole fashion industry. 2. Consumers quoted price consistently among the top 3 quality attributes for mid and high-level fashion brands in surveys over the last 5 years. 3. In a recent survey, over 80% of the existing customer base claimed that they would still buy more than 50% of their clothes from Zapclothing regardless of the price. 4. Female teenagers aged 20-30 consider price among the top three criteria for deciding whether to make a purchase. #### Method 1. Read the question carefully and make sure you understand what is being asked. 2. Scan the answers and underline the key words. Do not spend more than 10 seconds on this step, the purpose is just to make sure you are then quicker in finding the right part of the introductory paragraph. 3. Think carefully about how this proposal can be challenged. The most effective challenge is necessarily going to be that this proposal does not help to solve the company’s problems, i.e. it does not help to restore high revenues. 4. Go back to the answers, crossing out the wrong ones: 1. Not relevant. The fact that prices increased on average by 15% for the whole fashion industry does not tell us whether the decision to reduce prices will bring additional revenues from existing and/or new customers. FALSE 2. If consumers consider a higher price to be a signal for superior quality for mid and high-level fashion brands (among which Zapclothing is positioned), reducing prices could have a neutral or counterproductive effect on revenue growth. TRUE 3. Not relevant. It is immediately understood that this fact would be incomplete and thus not sufficient to challenge the sales manager's proposal: it focuses solely on revenues from existing customers. Even if nothing were to change in the purchasing behaviour of existing customers, there would still be the base of new customers to tap in. FALSE 4. Opposite direction. This fact would not challenge the sales manager’s assumption, but reinforce it. FALSE #### Tips & Tricks Right answers for root cause reason questions have two elements in common: • They are relevant - they have an effect on the target stated in the introductory paragraph. • They are going in the right direction - their effect on the target should be going in the direction stated in the question (support or challenge). There are usually three type of answer options for root cause reason questions: 1. Not relevant. These are answers that have no or limited effect on the conclusion/proposal, such as answers A and C in the example above. By identifying what sort of fact would challenge the conclusion/proposal, you’ll be able to isolate answers that have simply no influence or only a partial influence. In the latter case, do not assume anything that is not mentioned or clearly inferable logically and cross the answer out. 2. Relevant, but going in the wrong direction. These are answers that affect the conclusion/proposal, but the effect is going in the opposite direction. For example, answer D above is actually reinforcing rather than challenging the sales manager’s proposal. It is therefore essential that you always keep in mind what the question asks and what kind of facts would be effective in answering the question. One of the most common mistakes in root-cause reason questions is selecting answers that are relevant, but whose effect goes in a direction which is opposite to the one requested. 3. Relevant and going in the right direction. These are answers that affect the conclusion/proposal in the right manner according to the parameters set by the question. ### Fact-based conclusions (~17% of the PST) Fact based conclusion questions test your ability to draw logical conclusions from a collection of facts. Again, we also cover these on our course. Some examples are: Which of the following is TRUE based on the data presented in Exhibit 1? Which of the following can be concluded based on the information presented in Exhibit 2 about GDP growth? #### What is it? Fact-based conclusion questions test your ability to recognize and draw logical conclusions based on given a set of data/facts. This type of question probably has the greatest degree of variability: it can go from something very similar to “Reading facts” questions to challenging inferences from vague introductory paragraphs. #### Question Formats • Which of the following statements can be concluded from ...? • Based on the data on table xx, which of the following statements is a valid conclusion ...? #### Example Pharcom is a global pharmaceutical company engaged in the development of small molecule drugs for curing. Your team has been called by the Head of R&D to help him pre-select the drugs that are most likely to reach patenting and commercialization. He claims that on average 12% of researched drugs are cleared to be marketed, while the remaining part are dismissed either during the R&D process or final certification. Currently the average total expense for every drug in development is 12 Mn£ and the full trial and certification lasts for 10 years for the drugs going through the full process. The research and development process of the drugs is constituted by the following steps: 1. Trial 1: Laboratory trial to test the effect of the active ingredients. The trial costs 3.5 Mn£ and lasts for 2 years. 2. Trial 2: Laboratory trial to test the impact of side effects. The trial costs 4 Mn£ and lasts for 1.5 years. 3. Trial 3: Animal testing to evaluate bacteria resistance. The trial costs 4.5 Mn£ and lasts for 4.5 years. 4. Final certification by Food and Drug Administration. Filing costs 4.5 Mn£ and certification lasts for 2.5 years. Which of the following statements can be concluded based on the information above? 1. Most drugs complete the entire research, development and certification process. 2. Before being either approved or dismissed, drugs remain in the development and certification process for an average of 7.5 years. 3. Reducing by 50% the length of Trial 2 and Trial 3 would reduce the total cost of the Pharcom research and development process by 4.25 Mn£. 4. Over 50% of the drugs reach Trial 3 stage in the research and development process. #### Method 1. Read the question carefully and make sure you understand what is being asked. 2. Go through the answers and underline key words. Identify the graph or part of the introductory paragraph each answer relates to. 3. Start with the numerical answers. They are often the easiest and clearest to solve. Go back and forth between the answers and the introductory paragraphs/graphs. In order to identify the right answers, always think whether the opposite of the statement would be true. 4. Go back to the answers, crossing out the wrong ones: 1. The average time drugs are in the process before being certified or dismissed is 8 years, given by the average expense of 12 Mn£ that is reached in 8 years, after Trial 3. Take the extreme case to disprove it: if you assume that half of the drugs are dismissed after 7.5 years and half after 8.5 years, the average would be 8 years. In this case no drug would complete the full process. FALSE 2. From the solution above, the average time drugs are in the process before being certified or dismissed is 8 years, given by the average expense of 12 Mn£ that is reached after Trial 3 (3.5 in Trial 1, 4 in Trial 2 and 4.5 in Trial 3). FALSE 3. We simply do not have enough information to make such a conclusion. What if for example reducing investments reduces accuracy and prevents Pharcom from dismissing drugs that should not reach the next phase? FALSE 4. Trial 3 is reached after 3.5 years, the length of Trial 1 and 2. The average time drugs are in the process before being certified or dismissed is 8 years, given by the average expense of 12 Mn£ that is reached in 8 years after Trial 3. Taking the extreme example, such result could be achieved even if, for example, half of the drugs were dismissed marginally before 3.5 years and the other half after 12.5 years. However this is impossible, since the maximum length of the process is only 10.5 years. Hence, this implies that more than half of the drugs reach Trial 3. TRUE #### Tips & Tricks There are three possible types of answers that you may encounter in fact-based conclusion questions: 1. False conclusions - some conclusions may simply be false or wrong. Even if their logic is correct, the outcome may be reversed or wrong. 2. True conclusions - answers which both sound logic and draw the correct conclusion. 3. Unproven conclusions - the logic may be correct and the conclusion reasonable, however they are not supported by facts in the introductory graph or paragraph. #### How to tell false from true conclusions? Telling true from false conclusions may prove challenging and time-consuming. Some answers especially will require you to mentally estimate a set of values for which some statements or relationships can hold. Here are a few steps which may prove useful in assessing a statement: • Can the opposite also be true? Always evaluate whether the opposite of what is stated can be disputed. Candidates typically do not ask themselves this question. You’ll be surprised how asking yourself this kind of question can make a significant difference. • Consider the extremes Conclusions should always be true, not just most of the time. If a conclusion is not always true, it’s not valid. When dealing with ranges of numbers, select them so as to keep them as close as possible to the situation described in the statement, but do not comply with it. What would make it wrong? ### Word problems(~15% of the PST) Word problems questions ask you to solve business problems using data provided in the question and data from tables and exhibits. Some examples are: Assuming that a machine costs$2 m, how many years will be necessary for XYZ to break even from its investment?
If an average employee is paid 12 hours per month, which of the following formulae accurately calculates the average number of items handled per employee, per month?

#### What is it?

Whilst on most questions you get all the relevant data and information from exhibit or introductory paragraphs, in word problems part of the data is contained in the question itself, while another part in the exhibits or introductory paragraph. If you have taken the GMAT before, you will find that word problems are the closest question types to the GMAT.

#### Question Formats

• If employees’ salaries are increased by 20%, what is the increase in productivity required to break even?
• Assuming that the economy keeps on growing at 2% per year for the upcoming 10 years, which of the following equations best approximates the decrease in the debt/GDP ratio?

#### Example

Ardito, a leading fast fashion retailer, has 3,350 branches with 79,000 employees at these branches. Maison operates on approximately 25 FTE per retail branch. Approximately, how many more branches than Ardito should Maison have to sell as many clothes in Menswear as Ardito?

1. 500
2. 1,700
3. 5,000
4. 127,000

#### Method

1. Carefully understand the word problem.

2. Go through the answers to quickly assess the level of precision you will need in your calculations. Since all answer options are quite far apart, you will be able to estimate rather than calculate precisely.

3. Build up the structure of the equation.

What has to be kept constant?

$\text{Sales}\textsubscript{Ardito} = \text{Sales}\textsubscript{Maison}$

Hence, calling x the additional branches, Maison needs to sell as many clothes as Ardito:

$\text{Total employees}\textsubscript{Ardito}\ *\ \text{Sales per employee}\textsubscript{Ardito} =$
$= (\text{Branches}\textsubscript{Ardito}\ +\ x)\ *\ \text{Employees per branch}\textsubscript{Maison}\ *\ \text{Sales per employee}\textsubscript{Maison}$

Yielding:

$79,000 * 400 = (3350 + x) * 25 * 250$

At this point, we have two possible solutions.

First solution:

$\frac{79,000 * 400}{25 * 250} = 3,350 + x$

$\frac{79,000 * 16}{25 * 10} - 3,350 = x$

$\frac{79 * 100 * 16}{25} = 3,350 + x$

$79 * 4 * 16 - 3,350 = x$

$79 * 64 - 3,350 = x$

$~5,000 - 3,350 = x$

Thus the result must be between 1,000 and 2,000. Answer B.

Second solution:

You plug numbers from the answer options in the equation and see which result would make the equation work. This method is by far our preferred way of solving this king of problems.

$79,000 * 400 = (3,350 + x) * 25 * 250$

$~32,000,000 = (3,350 + x) * 6,250$

1,700 is the only result fitting the equation. Answer B.

### Client interpretation (~10% of the PST)

Client interpretation questions focus on understanding project requirements and the analyses necessary to tackle the client’s issues.
Some examples are:
Which of the following most accurately describes the reason for the team's project?
Which of the following best summarizes the CEO’s concerns?

#### What is it?

In consulting projects, you will engage every day with various stakeholders from the client. Essentially, client interpretation questions are about understanding:

• What the client says that can have an impact on defining the scope of your projects,
• What the client implies about given choice or strategy,
• What are the best analysis decisions to take in order to fit the client’s needs.

#### Question Formats

• Which of the following best summarizes the CEO’s concerns?
• Which of the following statements best describes the thoughts of the CEO regarding...?
• Based on the opinion of the Head of Department, which of the following statements is/are valid?
• Which of the following statements best describes the CEO’s aims for the McKinsey study?
• Which of the following analyses would be LEAST useful to address the CEO’s concerns?
• Given the aims of the CEO, what would be the LEAST relevant question for the team to answer?

#### Example

Topstar is a leading fashion retailer of clothing, shoes, make-up and accessories. It has around 400 shops worldwide, of which 200 are in the UK. Topstar operates through a franchising model, where shops are run by private independent companies and pay a royalty fee to Topstar. In exchange, Topstar designs the shops and supplies them with updated clothing lines, manages branding, sets advertising and promotions, and provides shop-owners with guidance on all standard operating procedures for running the shops. Even if this strategy enabled Topstar to dramatically grow in scale, boosting shop opening and customer base, customer numbers have recently plateaued, and this has resulted in slower sales and profit growth.

The CEO of Topstar has engaged your team to help better understand whether the recent changes in revenue and profitability trends are related to unsatisfactory shopping experience. He is convinced that the recent growth in scale came at the expense of a consistent shopping experience across all shops. He tells the team “I am sure that the responsibility of the current slowdown lies in poor delivery by the shop owners. I recently visited 5 shops in different countries and 3 of them did not fully apply our policies ensuring consistency in shop layout and pricing policies. This is disorienting our customers and pushing them to seek out our more and more aggressive competitors”.

Which one of the following answers BEST describes why the CEO has engaged your team?

1. He wants help in implementing a coherent and consistent brand image and shopping experience across all shops.
2. He wants to identify the causes of the inconsistent shopping experience across shops in different countries.
3. He wants to validate his hypothesis that an inconsistent shopping experience in different stores led to declining revenues and profitability.
4. He wants to overhaul the set of policies and standard operating procedures imposed to shops in order to guarantee a consistent shopping experience.

#### Method

Approach these questions using our established method. Two aspects of our method are particularly relevant:

1. Read the question. Pretty straightforward, asks for the reason of the engagement.

2. Scan the answers and underline key words. Do not spend more than 10 seconds doing this step. The purpose is just to be as quick as possible in finding the right part of the introductory paragraph.

3. Go back to the text and quickly jump to the relevant part. More than 50% of the paragraph is useless or only marginally useful. Precisely reading the essential sentence will be enough to answer the question.

4. Go back to the answers, crossing out the wrong ones:

1. This answer may be true, but it does not illustrate the purpose for the engagement of your team. The CEO did not call the team to advise him on branding or design, but on understanding the causes of the downturn. FALSE

2. The purpose for the engagement of your team is not understanding the causes of the poor shopping experience, but the causes of the downturn. FALSE

3. The purpose of this engagement is finding out whether inconsistent shopping experiences across stores led to the current downturn. TRUE

4. Again, this answer could be true, but it is not the purpose for the engagement of your team. The CEO did not call the team to redesign policies, but to understand the causes of the downturn. FALSE

#### Tips & Tricks

• Highlight keywords in all answers. Prioritizing the right words and sentences will save you a lot of time.

• Cross out wrong answers. You will often find that at least 2 answers look correct or almost correct. At this point go back to the introductory paragraph with the two “almost right” answers in mind and pick the right one based on the true meaning of the introductory paragraph.

• Beware of the “sensible answer trap”. Sometimes answers contain implications that look rational and sensible. However, if the client did not say it, they are not the valid answers.

### FORMULAE (~5% of the PST)

Formulae questions will ask you to express a quantitative word problem as a symbolic formula.
Some examples are:
Which of the following formulae calculates the share of non-performing loans out of total loans?

#### What is it?

Formulae question test your abstraction capabilities. Are you able to extrapolate a trend or a result from a set of data? Are you able to break down problems, identifying drivers and directions of causality?

#### Question Formats

• Which of the following formulae best approximates ....?

#### Example

Forman Fisheries is engaged in packaging shrimp and other fish. There are four grades of shrimp, from A to D, reflecting their size and taste. Below are some key productivity indicators for Forman Fisheries in the shrimp packaging activities:

2012
Grade A shrimps packed in a month (a) 3,600
Grade A shrimps share of total shrimps (b) 12%
Total boxes per year (c) 8,900

Assuming that all boxes contain the same quantity of shrimps, which of the following formulas best approximates how many boxes of non-grade A shrimps were packed in the last month?

1. $\frac{a}{12*b*c} * (1-b)$
2. $\frac{a}{b*c} * (1-b)$
3. $\frac{a*b}{(1-b)*c} * 12$
4. $\frac{c-cb}{12}$

#### Method

1. Homogenize your measuring units. Since we are looking for months, wherever we will need the quantity of total boxes (c), we’ll divide it by 12, since it is a yearly indicator.

2. Break down the problem into smaller steps that help you get to the ratio, in this case:

$\text{Boxes on non-grade A shrimps} = \frac{\text{Number of non-grade A shrimps}}{\text{Shrimps per box}}$

Identify how to solve this for each of the factors in the equation:

$\text{Number of non-grade A shrimps} = \text{Total shrimps}\ *\ \text{Share of non-grade A shrimps}$

$\text{Total shrimps in a month} = \frac{\text{Grade A shrimps packed in a month (a)}}{\text{Grade A shrimps share of total shrimps (b)}}$

$\text{Share of non-grade A shrimps} = 1\ -\ \text{Grade A shrimps share of total shrimps (b)}$

$\text{Shrimps per box} = \frac{\text{Total number of shrimps in a month}\ (\frac{a}{b})}{\text{Total number of boxes}\ (\frac{c}{12})}$

Therefore:

$\text{Boxes on non-grade A shrimps} = \frac{\frac{a}{b}(1-b)}{\frac{12*\frac{a}{b}}{c}}$

Simplifying:

$\text{Boxes on non-grade A shrimps} = \frac{c(1-b)}{12}$

#### Tips & Tricks

Formula questions are about extrapolating a formula that should work with all numbers. However, sometimes answers are presented through formulas with numerous simplifications that might make it difficult to tell whether the numbers are correct. A trick that could work in order to double-check results is replacing numbers in the table with simple ones, coming up with a solution and then plugging it into the answer options to see which one gives the right result. For example in this case, assume:

• Grade A shrimp share of total shrimp (b): 10%
• Total boxes per year (c): 1,200 (or $\frac{c}{12} = 100\ \text{monthly}$)

Since all boxes have the same size, non-grade A boxes will be $(1 - 10\%) * 10 = 9$.

If you know that all your results should be 9, plug in the numbers above in the answer options above and check in which of them you get 9. This trick works very well when the formulas involve high degrees of simplification.

## How to prepare for the McKinsey PST: plan and test strategy

Devising a solid preparation plan and test strategy is essential to be successful. In the following sections we will guide you through a very efficient preparation plan and will give you some very important advice on test strategy.

### Preparation plan

Don't be fooled by those who say "Practice,practice, practice". While practicing is very useful, brute force practice can be quite ineffective.

A smarter and effective preparation plan involves:

1. Assessment

You need to see where you stand and what your improvement areas are. The best way to do this is to do a test. Don't worry about your score, you will simply need it to see where you stand. You can use a McKinsey test or one of ours. Then categorise questions and see where you are lacking. If you purchase one of our packages, we do that for your already so you will not have to go through it.

2. Skill building

Work on your improvement areas. In particular, you should focus on the following:

• Identify root causes and draw fact based conclusions
We provide 10 specific questions each in our Test Ready and Beyond Test Ready packages; our case academy also features 2 exercise sections where you will be able to find 15 questions each (30 in total).

• Numerical agility
An essential skill for the PST. The math video in our case academy (efficiency tools) will provide all the fundamentals and tips and tricks to be fast with numbers. Being able to make estimates in the PST is very important. This includes understanding the required degree of approximation and performing the calculations fast. Our mental math tool can be very useful to practice.

• Reading charts and solving problems
This one is again very important, covered in our case interview course as well, both theory and practice. Extensive drills are included in our Beyond Test Ready package.

3. Perfecting

Once you feel comfortable with the skill level you are at, you will then have to start practising on actual test questions. There are not many quality questions online so you need to be efficient. You will use 1 test at the beginning to assess your level, and you should keep 2/3 at the end for test simulations. Since there are not many quality questions online, it is important to use available material efficiently in this stage. We advise to do a test, identify your improvement areas, then work on the specific questions provided in in our Beyond Test Ready package and go back to the fundamental skills if you need so.

4. Simulation

#### Keep an error log

When reviewing your mistakes, everything looks clear and easy. However, 2 weeks later, you encounter a question with the same structure as another one that you previously got wrong and you become puzzled: you have no clue how to start solving it. This is what the error log is for: keeping track of your mistakes and what've you found the hardest, in order to go through it all frequently (e.g. every two days) and consolidate your technique. An error log is a continuous method of analysing practice problems to identify WHY you answered them incorrectly.

Error logs are a very effective tool for preparing to GMAT or other exams, but we recommend you to use them also for the Problem Solving Test.

There is no single right or wrong format for the error log. Some people like using detailed spreadsheets, while others simply use a paper, a pen and a symbol guide for marking and tracking certain answers. We recommend a simple, effective structure that you can use on paper or Excel / PowerPoint:

• Question type (you will see our breakdown by question types below).
• Reason why you've found the question difficult. Usually it’s either about taking too long to answer or not being able to answer at all.
• Proposed solution. The solution you find the quickest and the most effective.
• Key takeaways. What you should learn in order to answer that type of question more efficiently, e.g. learn to quickly simply fractions or improve your quick reading skills.

The “key takeaways” part of the error log will also constitute your to-do list for the coming days of the preparation.

Another reason why an error log is pivotal to PST success: there is a limited quantity of high quality questions. While the official McKinsey test provides excellent preparation and we too have invested a lot of money in making and testing content, the number of available tests is still limited. By keeping an error log and completing the necessary analysis, you will take full advantage of each question. Extra practice is always the best way to improve, as being exposed to different questions can help you identify your improvement area. Visit our PST practice page to find out more about extra practice.

### Test strategy

The majority of PST questions is not very conceptually difficult; the real challenge comes from the time constraint. In this section we will go over a test time strategy and a consistent method to answer questions to make sure you don't waste any time.

#### Time strategy

Some questions in the PST look exceedingly complicated. Sometimes it may even look like if you give each such question the time it seems to require, you might run out of time on a single one! Spending excessive time pouring over hard questions often prevents candidates from leaving enough time for other, more straightforward questions. And, since you do not need to answer all of the questions right in order to pass the test, this strategy is dangerous and counterproductive. The strategy we suggest is all about allocating the right amount of time to all the questions and to copying answers at the end:

• Keep at least 5 spare minutes at the end of the test to copy your answers on the answer sheet. If you have 60 minutes in total, you’ll be left with 55 minutes.

• Break down the remaining time in minutes per question - in this case about 2 minutes per question.

Two minutes per question is an extremely challenging time horizon by itself. Successful candidates tend to develop a structured and consistent approach to answering PST questions over the course of their training. Whilst we advise to adopt a slightly different approach based on kind of each questions, these guidelines provides a simple and straightforward approach that can be applied to any question, allowing you to quickly build good habits. Do not take this advice as a rigid framework to follow but rather as a starting point to develop the strategy that suits you best.

Here’s our method in a nutshell:

1. Carefully read each question. Read the question in detail, understanding what kind of answer the test is looking for. By reading the question, you will scope out what the question is looking for in the introductory paragraph. Even if starting by quickly skimming the test may sound tempting, refrain from doing so: you are wasting precious time and at least 70% of the introductory paragraph is about context information that is not relevant to the question asked.

When you start practicing, you will realize that at least 20% of your mistakes are due to misread questions.
2. Quickly skim through the answers and underline key words. Going through the answers will give you additional information about the question and the possible alternatives for answering it. Such information is be very important when dealing with qualitative answers, but even more so when dealing with quantitative answers:

• Qualitative answers: underline key words such as verbs and adverbs like “never” or “always”, which can usually help you to rule out some answers. Answers containing “always” or “never” that generalize a trend should raise a red flag, since they are less likely to be the right ones.

• Quantitative answers: understand what degree of simplification is necessary - or, in other words, understand whether you are dealing with a precise maths question or an estimate maths question. If, for example, all answers are very close and distance themselves by few units or percentage points, you must be accurate in your calculations. If, on the other hand, there are big gaps between the provided values, you’ll be able to round numbers and simplify your calculations.

The PST tests your ability to cope with ‘information overload’, i.e. dealing with a large amount of data that may not help in answering the question.
3. Identify and understand relevant text and data. Understanding what information you need to get and what level of detail is required, will enable you to quickly identify the relevant part of the introductory paragraph or the relevant data in exhibits/tables. Read it carefully, underlining, if necessary, key words and try to figure out the answer to the question in your mind.

4. Pick the best solving technique. Basing on the question's type, choose which technique is more appropriate:

• Qualitative answers: Follow an iterative process of eliminating wrong answers by going back and forth between the relevant section of the introductory paragraph and the questions. If, while scanning through answers in phase 2, you underlined key words, your work will be simplified. Even if you feel like you've identified the right answer, always go for the elimination strategy: a qualitative answer is not true until you have eliminated all the alternatives. The reasoning behind this strategy is that often at first sight some answers look less straightforward or more complicated, but on closer inspection they turn out to be the right ones. You’ll find additional techniques for solving all types of qualitative questions in the next paragraphs.

• Quantitative answers. Identify the best technique by choosing between:

1. Identifying relevant data and solving the problems directly by running all calculations on paper and ascertaining which answer matches with the results of your calculations.

2. Building a framework of the calculation and plugging in the suggested answers until you find the one that works. Usually, once you find the answer that makes your framework/equation work, there is no need to test it with other answers.

## Ready for the McKinsey PST?

Enough theory for now! Time to start practicing with our free test.
We suggest printing it out to replicate a real test environment.