Maths skills on the job

maths project skills
New answer on Nov 16, 2020
4 Answers
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Anonymous A asked on Jan 19, 2018

Hi All,

Wondering how much maths is actually done on the job by hand? Case prep seems to emphasise the ability to handle maths by hand, however in the real world on a project, how much is done without the support of Excel or a calc? Obviously, there are times when we must estimate a figure with the client in the initial stages or in question stage, but surely 90% is done (away from the client) on the computer?

Furthermore, it appears teams are multidisciplinary in nature; does this mean that there is generally a quant team member who would specialise in the number crunching, while there could be others weaker in maths skills, who help provide structure, direction, qualitative insights etc?

Many thanks.

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replied on Jan 19, 2018
Former BCG Principal and decision round interviewer

Agreed with other answer. The one thing I would add is that a skill that is critical on the job is what I would call "number sensitivity" for a lack of better description. This skill straddles between the domains of math, memory and business judgement.

At its essence "number sensitivy" it's the ability of the consultant to understand the relevancy/importance of a number very quickly (e.g. during a conversation, within the first 5-10 seconds s/he looks at a document) and therefore being able to ask follow up questions on it in the moment and find the root cause of an issue more efficiently. To do this the consultant usually needs to have the following:

-very good memory of all relevant client, competitor, adjacent industry key metrics

-ability to do simple math in his/her head quickly

-good business judgment to understand whether that number might be (or not be) the culprit of problem at hand

To give an example: if during week zero of a case during interviews with the executive team one of the interviewees says that in their product development team 10 people out of 30 left in the last 12 months, the consultant should be able to discern whether this is a ratio that is in the norm or is high or low and asks follow up questions on it if relevant or move on to other insights. Average consultant would take note and come back to it later once s/he does the research and understands the relevancy of that number.


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replied on Jan 19, 2018


As you may already suspect, most of the math isn't indeed done by hand, however any consultant (despite its level of seniority) needs to be able to perform the most basic math operations quite quickly (eg, quite rough back of the envelope estimates in client or team meetings, where you’re not going to say: wait just a minute because I need to go to the computer to do the math). That’s why consulting interviews focus this, as it’s a relevant skill to possess even if you don’t use it every single day.

No, at least in MBBs there is no such thing as number crunchers, every consultant (in the generalist paths) is expected to be a well rounded one and performing well across the several dimensions (math/quantitative, problem solving, structure, etc)



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Content Creator
replied on Nov 16, 2020
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut


It´s a legit question!

I was surprised to see how much I did use mental math back in McK (e.g., to do a back-of-the-envelope calculation, run some "quick numbers" or stress-test to something, etc.) Hence, ti´s important

Hope it helps!



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Anonymous updated the answer on Aug 23, 2020

Hi A,

In the actual life maths skills are not that important. Especially that you will be having all the access to the modern tools like Excel, calculator, etc. But during the the recruiting that important that you have good quantitative skills. It's one of the selection criteria. So to answer your question, don't stress that much, you will be able to access to all the tools in the real work and it won't be expected that you can counrt everything in you head.

As you rightly mentioned that teams are diversyfied, so if you are working on a quantitative heavy project it's always good to have quantitative guy who can crunch the numbers, which is pretty often the case.

Hope it helps,




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Andrea gave the best answer


Former BCG Principal and decision round interviewer
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