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Division Estimation

case math
New answer on Oct 06, 2020
2 Answers
Anonymous A asked on Oct 05, 2020

Hello, I want to ask a question that seems a bit silly, but kind of bugging me lately! Sometimes while doing cases we get divisions like this (544/ 63) or (710/ 82) or something similar, if I try to calculate them precisely they would take so much time (tbh I don't know how to calculate them precisely). I will do fine with a simpler division but this kind of divisions kind of bug me, so the question is:
1- Is it usual to estimate while doing some divisions? or I need to calculate the exact number?
2- If I do need to calculate the exact number, is there any method or video you guys recommend? I searched over youtube and some other places, they have basic division techniques, as for the more complicated divisions, they usually recommend using a calculator, so what do you guys think?
Thank you very much!

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Content Creator
replied on Oct 05, 2020
#1 BCG coach | MBB | Tier 2 | Digital, Tech, Platinion | 100% personal success rate (8/8) | 95% candidate success rate

In general, ask to round if the numbers seem unmanageable. Say something like "I'm going to round this number to 100 if that's ok". If they say no, then of course you're ok to write down the math!

Leverage the free preplounge resource:

Rocketblocks is great for math in the context of a case:

Print out math sheets for rote practide:

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Content Creator
replied on Oct 06, 2020
McKinsey offers w/o final round interviews - 100% risk-free - 10+ years MBB coaching experience - Multiple book author

Hi Anonymous,

In general there is no right or wrong way to do this calculation. It really depends on 1) the situation and 2) your communication (yes, really).

ad 1) Let's assume you need to compare 3 different options and all 3 of them have rather similar numbers. In this case it won't help you a lot to do a rough estimation, because if the numbers are very close from which you start, an approximation won't give you the exact order of those 3 options, so you would miss the whole point of this comparison.

In other words, if a ballpark number is good enough to proceed further in the case and know which direction to go, an estimation is perfectly fine. Sometimes this is difficult to judge from the candidate's perspective - whenever in doubt just ask the interviewer if he is fine with that estimation!

(Unless I have doubts in general that you are comfortable with numbers and want to ensure that you can do math - in this situation I will nevertheless push you to do it accurately. Yes, some shortcuts exist, but it's also possible to do it rather quickly on paper without shortcuts, just a matter of practice.)

ad 2) The actual calcuation is one thing - the exact way how you communicate it is another thing. It's definitely a relevant mistake to answer this mathematical question by doing an approximation and then present it just as the solution to this math question, without mentioning your estimation. So be very explicit in the way how you calculate the number and ensure that the interviewer is explicitly aware of that.

Hope that helps - if so, please be so kind to give it a thumbs-up with the green upvote button below!


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Ian gave the best answer


Content Creator
#1 BCG coach | MBB | Tier 2 | Digital, Tech, Platinion | 100% personal success rate (8/8) | 95% candidate success rate
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