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When is it OK to estimate? Is a fast estimate better than a slow but accurate answer?

case math estimation mental math
Recent activity on Apr 04, 2018
2 Answers
3.3 k Views
Anonymous A asked on Apr 03, 2018

I understand that it is generally OK to estimate when you are using a calculation to get a Y/N answer (i.e. determining whether to proceed/not proceed based on being above or below a specifc target).

Other than this situation, is it OK to round or estimate your answers to get an approximate answer more quickly? Do I need to ask the interviewer every time I want to round or estimate slightly [e.g. rounding (155 million / 206) to (155 million / 200)]?

Also, if specifc answers are required, what level of precision is generally acceptable? One decimal place?

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replied on Apr 04, 2018
McKinsey / Accenture Alum / Got all BIG3 offers / Harvard Business School


  1. Ask the interviewer 1-2 times to get a sense of how comfortable he is with rounding numbers and how many zeroes he requires.
  2. Continue with an assumption that you should keep that level of preciseness throughout the case. Worst case - he'll tell you to change the approach


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replied on Apr 04, 2018


First, I would never estimate (other than direct market sizing questions!) without asking first if the interviewer has such data available. If he doesn’t have it, then it’s a hint that you might need to estimate.

Second, you should never make approximations without asking if you can do it. You’ve no idea which skills the interview is trying to test, if it’s pure math, you don’t want to be the person who decided to simplify all the math (ask also about the decimals, but it’s rare to have cases working with decimals)



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Vlad gave the best answer


McKinsey / Accenture Alum / Got all BIG3 offers / Harvard Business School
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