Techniques for division?

Case Calculations Division maths
New answer on Jun 09, 2020
7 Answers
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Anonymous A asked on Jun 07, 2020

I find my case math division skills are generally ok. I have learned the division table up to 1/11 and find it very helpful for divisions with a single digit diviser.

My main issue is when I am dealing with a multi digit diviser (e.g. 25k / 42 or 825 / 76) because I usually take quite a long time to do the calulation and it is not often accurately done.

What techniques do others use for these sorts of problems?

Thank you very much.

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Vlad
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updated an answer on Jun 08, 2020
McKinsey / Accenture Alum / Got all BIG3 offers / Harvard Business School

Hi,

I recommend learning a division table. Learn all the numbers until 1/10 (e.g. 1/3 = 33.3%, 1/4 = 25%, 3/4 = 75%, 1/6 = 16.7%, etc)

This method will help you calculate any percentage problems like market shares or margins. For example, if your market is $620M and your revenues are $5.1M you can use 5/6 or 83.3%, as a proxy to calculate the market share. By adjusting to zeroes and slightly decreasing the number, you'll get 8.2%

Best

(edited)

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Anonymous updated the answer on Jun 07, 2020

Hi there,

I agree with David, most interviewers would be fine if you just round the denominator to make the calculation slightly easier (it is all about being 80/20) - if the interviewer insists against the rounding, then it's normal to ask to solve it by hand.

Best of luck in the process.

Khaled

(edited)

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Anonymous replied on Jun 07, 2020

Hello,

Maybe other people will have better ideas than me on this, but I fear that certain divisions must really be put on paper. But I still advise you to propose rounding to your interviewer before embarking on complicated calculations (e.g. divide 25k / 40 vs. 25k / 42).

Best,

David

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Clara
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replied on Jun 08, 2020
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut

Hello!

Whenever you find those odd divisions in an MBB/consulting interview, be careful. It´s precisely a trap to see if you can simplify.

For instance, to your examples:

  • 25,000 / 42:
    • Round up 42 to 40
    • 40 is 4/10, or 2/5
    • Now it´s much easier:
      • Divide 25,000/5
      • Then multiply per two

Hope it helps!

Cheers,

Clara

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Antonello
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replied on Jun 09, 2020
McKinsey | MBA professor for consulting interviews

Hi, in addition to all the advices of other coaches I recommend this YT channel - very useful for divisions and math tricks in general:
https://www.youtube.com/playlist?list=PLjbxBzUM6SLnSYop8JXLu9zciW-rn7yyD

Hope it helps,
Antonello


Ps. Preplounge math tool then is great to practice it: https://www.preplounge.com/en/mental-math.php

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Anonymous updated the answer on Jun 09, 2020

Dear A,

You can make your calculations easier with round the last number or for division process itself you can put asid all the nulls (but then don't forget to put them back).

Like 25k/42

25 000/40

25/40--> 24/4---> 6

600 appr

Whould it be ok?

Good luck,

André

(edited)

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Ian
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replied on Jun 09, 2020
BCG | 100% personal interview success rate (8/8) and 95% candidate success rate | Personalized interview prep

Hi there,

I highly recommend the following resources:

  • Online "Drills": https://www.jetpunk.com/quizzes/fast-math-multiplication-quiz
  • Math sheets (print these and do them on paper): https://www.math-drills.com/
  • Rocketblocks: https://www.rocketblocks.me/
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Vlad gave the best answer

Vlad

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