ex-Manager - Natural and challenging teacher - Taylor case solving, no framework
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Math Question During Interview

Anonymous A

Hi everyone,

During an interview, the interviewer will ask us some sudden math question so how long do we have to calculate it ? Can we write it down to a paper and calculate the number ?

During solving case, can we write down our math calculation or it has to be 100% estimate in our mind ?

Thank you so much,

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Benjamin replied on 09/13/2018
ex-Manager - Natural and challenging teacher - Taylor case solving, no framework


When performing a calculation, I recommand :

  • Split the discussion in two : start with the structure of the calculation, and once it's validated draw hypothesis and perform the calculation
  • when perofrming the calculation, we don' t expect you to be supper fast, be at least to be accurate. So in case, it's super direct, you should ALWAYS write down on the paper the calculation. I also recommand to proceed with intermediate steps in the calculation so it will be easier to correct in case there is a mistake.


Vlad replied on 09/13/2018
McKinsey / Accenture / Got all BIG3 offers / More than 300 real MBB cases / Harvard Business School


You SHOULD write down the numbers and come up with the approach to calculations. Some of the calculations you will calculate mentally, others (e.g. equations) you will actually do on paper.

Overall you should follow the following algorithm:

  1. Always tell the interviewer your approach
  2. Check with the interviewer that your approach is correct
  3. Do the calculations writing down the numbers and doing the simple calculations mentally. Come to the interviewer with some preliminary answers
  4. Check your answer with the interviewer