How to communicate a complicated math question in a virtual interview?

New answer on Jan 27, 2022
3 Answers
Anonymous A asked on Jan 26, 2022

Hi guys, I would like to seek advice on how to communicate a complicated math question during a “virtual interview”. Usually, I prefer to “speak out loud” if the math equation is quite simple. However, I ran into a situation where there were multiple data sets including different revenue sources, cost items, startup cost items, and I needed to calculate a “payback period”. I feel that my communication was not streamlined and clean. 

My questions are (1) in such a complicated situation, is it always better to communicate/go through the overall “ calculation structure” before calculating? I did this today but the interviewer asked me to directly show him the calculated result instead of spending time to explain the math framework. (2) is it better to “calculate in silence" or should I “do the calculation out loud”? I usually lay out the math formula first then mention something like rev = A*B*C and then conduct the calculation. But again, it seems that the interviewer just wants to know the result and do not want to know how I got to the details. 

Could you please show some advice on how to improve communication for complicated math questions? Are there some ways to improve this weakness and sound “structured” in complicated math caculation? Thank you!

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Content Creator
replied on Jan 26, 2022
McKinsey | 100+ coachings & interviews @ McKinsey | ESADE MBA | Top rated for experienced hires & career transitioners

Ultimately, you will just have to do what the interviewer tells you to. However, I think your instincts are right!

With anything numerical, there are typically 3 stages:

  1. Verifying objective: When you are presented with a bunch of data, numbers, own estimates, etc. you will have to decide what to do with it. This is more challenging in candidate led cases, where you're “in charge". In that case, consider overall case objectives, your framework (don't just start random calculations), and what numbers are available. Then verbalize what it is you would like to calculate and why. Not sure if you did that but you should (unless this part is explicit in the case e.g. client wants you to calculate a payback period for investment x).
  2. Verifying approach: Once your interviewer is on board with the objective, you need to figure out how to get there. That's basically your equation, which ideally includes variables that you have data for. Verify with the interviewer by verbalizing top down. If he wants you to just get on with it, that's what you'll do. If he pushes back, keep composed and explore what's wrong (that's why you verify in the first place instead of going down the wrong route).
  3. Execute: This is where you can go silent once you politely ask for some time. I never expect candidates to talk me through the actual number crunching because it's not effective. Maybe communicate some partial results to break the silence from time to time. Other than that, the objective is to be quick and correct, not chatty.

Hope this helps figuring out you own strategy! Best of luck!


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Content Creator
replied on Jan 27, 2022
BCG | 100% personal interview success rate (8/8) and 95% candidate success rate | Personalized interview prep

Hi there,

I recommend the following steps:

  1. State what you'd like to calculate and why (i.e. how it will help to solve the problem)
  2. Ask/take a moment to come up with the formula
  3. Articulate the structure to the interview (I will multiply this, then add this, etc.)
  4. Go and silently do the math
  5. Pop your head up at intervals to give a # update if the calcs are particularly long/complex
  6. State the final number and the impact/insight

To answer your question: 1) Yes go through the structure first and 2) Yes calculate silently


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replied on Jan 26, 2022
# Bain | EY-Parthenon | Roland Berger | FIT | Market Sizing | Former Head Recruiter

In general, you should confirm the approach first before moving on to the calculation. Of course, if the interviewer doesn't want to know, you'll have to accept that (maybe the interviewer thought that it was something straightforward?)

Regarding calculations it's the opposite. The interviewer won't even pay attention, and is not expecting you to go through each calculation. If the interviewer already knows you are calculating 7*15*350, the intermediate calculations are unnecessary, you just need to provide the right end result.

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Moritz gave the best answer


Content Creator
McKinsey | 100+ coachings & interviews @ McKinsey | ESADE MBA | Top rated for experienced hires & career transitioners
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