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 nongrade A shrimps were packed in the last month?
Method
 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.

Break down the problem into smaller steps that help you get to the ratio, in this case:
Identify how to solve this for each of the factors in the equation:
Therefore:
Simplifying:
And thus the correct answer is answer D.
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 doublecheck 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 )
Since all boxes have the same size, nongrade A boxes will be .
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.