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

Mental math - division

Hi everyone,

I feel pretty confident in my mental math skills, but sometimes I need additional time with division. Could you give me some hints for examples below.

-2.3/3.6 - I would multiply by 10  - 23/36 ≈ 60%

-70/85% - no clue for a shortcut

-707k/ 18 910 -  7 * 10^5 / 1.89 *  10^4 -- I know it is between 3.5 and 4, but don't know the exact

-88/1400 -- ?

Would love to hear your mental processes, thank you!

4
2.4k
8
Be the first to answer!
Nobody has responded to this question yet.
Top answer
Vlad
Coach
on Sep 17, 2019
McKinsey / Accenture Alum / Got all BIG3 offers / Harvard Business School

Hi,

Simply learn the division table up to 1/11 (i.e. 5/6 = 83.3%). It will help you calculate any percentage problems. For example, if your market is $620M and your revenues are $51M you can use 5/6 as a proxy to calculate the market share

Best!

Anonymous C
on Nov 16, 2020

On top of learning table up to eleven, but actually you only need the table of 2,3,5,7 and 11 the rest is useless as you'll simply derive it from the other one, one thing that usually helps is to multiply.

One thing that i noticed is that people have usually less trouble to estimate fraction bigger than 1 than smaller than one. For instance they would have less trouble to estimate 12/7 than 6/7.


So my advice would be to multiply to obtain something more convenient.
Another advice is to split your division.

23/36? Ok that's 20/36 +3/36. The first sum is half of 40/36 so half of 36/36+4/36. So 1+0.1+0.01+.... So 1.1 to call it short. The second part is 1/12 so 8.5%.

So practice that gymnastic both for mental calculation and on paper. During an interview, if you do this quickly on paper while at the same time explaining your process, your interviewer will actually prefer it much more than having a hard time to follow you because you do a lot of fast calculation in your head.
 

1
Anonymous B
on Oct 21, 2019

There is just one thing: practice, practice, practice, ...

0
Clara
Coach
on Nov 16, 2020
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut

Hello!

On top of the 11 table advise -which applies to many issues-, I wouldn´t stress to much, since you won´t get this complicated ones in an MBB interview. 

Hope it helps!

Cheers,

Clara

Similar Questions
Consulting
Advanced comments
on Jun 01, 2025
Global
6
100+
Top answer by
Hagen
Coach
#1 recommended coach | >95% success rate | 8+ years consulting, 8+ years coaching and 7+ years interviewing experience
8
6 Answers
100+ Views
+3
Consulting
GMAT/Conceptual Questions in MBB Case Interviews?
on May 26, 2025
Global
9
300+
Top answer by
Anonymous
20
9 Answers
300+ Views
+6
Consulting
I can not catch up with what the interviewer is saying
on Feb 28, 2025
Global
8
1.1k
Top answer by
Hagen
Coach
#1 recommended coach | >95% success rate | 8+ years consulting, 8+ years coaching and 7+ years interviewing experience
72
8 Answers
1.1k Views
+5