Schedule mock interviews on the Meeting Board, join the latest community discussions in our Consulting Q&A and find like-minded Interview Partners to connect and practice with!
Back to overview
Anonymous A
on Mar 05, 2020
Global
Question about

Mental calculation?

Would the interviewer expect mental calculations to solve this case? If so, would it be fine to work with rounded numbers?

2
6.0k
33
Be the first to answer!
Nobody has responded to this question yet.
Top answer
Sidi
Coach
on Mar 05, 2020
McKinsey Senior EM & BCG Consultant | Interviewer at McK & BCG for 7 years | Coached 400+ candidates secure MBB offers

Hi!

This is one of the many nonsense-myths flying around! MBB interviewers NEVER expect mental math! The only thing expected is that you can perform calculations in a clear and correct way, while taking along (!!!) the interviewer! This means that, apart from super easy calculations, you should always do rock-solid written calculations! NOBODY is interested in your mental math skills! It is NOT a relevant category in assessing a candidate's performance, and every MBB interviewer is explicitly trained on that. The interviewer will assess you on whether you are accurate and clear

In the extreme, very fast mental calculations are even very detrimental to a candidate's performance. Here's why: The interviewer will always assume that the way you behave in an interview is indicative of how you would behave with a client. So if you do all sorts of complicated math stunts in your head - guess what? You become extremely difficult to follow for the client! And at that point it becomes completely irrelevant whether your result is correct or not. If it is hard to follow your analysis, then your performance is poor. End of story.

Cheers, Sidi

Anonymous A
on Mar 05, 2020
Thank you very much for your answer. Do you think it would even be allowed to work with a calculator as the numbers of this specific case are really large and not even.
Sidi
Coach
on Mar 05, 2020
McKinsey Senior EM & BCG Consultant | Interviewer at McK & BCG for 7 years | Coached 400+ candidates secure MBB offers
Not in traditional 1-on-1 interviews. In written cases it varies between firms.
Luca
Coach
on Mar 08, 2020
BCG |NASA | SDA Bocconi & Cattolica partner | GMAT expert 780/800 score | 200+ students coached

Hello,

The only thing that is mandatory during the interview is to not do any mistake in your calculations.
Having said that, doing some mental calculation could really impress your interviewer, but do it only if you are sure of the result. You can even give a result doing fastly the mental calculation with rounded numbers and then write down the calculation with the exact numbers.

Best,
Luca

Similar Questions
Consulting
SUPER confused on this one Math Question, help please !
on Apr 03, 2025
Global
4
400+
Top answer by
16
4 Answers
400+ Views
+1
Consulting
Question about
How you calculate the total profits?
on Dec 12, 2024
Global
1
800+
Top answer by
Shane
Coach
ex-BCG London Principal 7yrs | 1st & 2nd round interviewer (150+) | CV screener | Recruiting mentor | LBS MBA
40
1 Answer
800+ Views
Consulting
Does mathematical accuracy matter while solving cases in an interview? How do I enable myself to do faster calculations?
on Nov 30, 2024
Asia
6
1.3k
Top answer by
Hagen
Coach
#1 recommended coach | >95% success rate | 8+ years consulting, 8+ years coaching and 7+ years interviewing experience
85
6 Answers
1.3k Views
+3