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

Any good tips on how to speed up division calculations? e.g. large number divided per 365 to receive daily amount

Is it accurate to use 350 instead of 365 for the numbers of days per year?

3
1.8k
22
Be the first to answer!
Nobody has responded to this question yet.
Top answer
Ian
Coach
edited on Jul 02, 2021
Top US BCG / MBB Coach - 5,000 sessions |Tech, Platinion, Big 4 | 9/9 personal interviews passed | 95% candidate success

Hi there,

Let me help with some tricks. Let's say we have to solve 1,000,000 / 1,800. We can do the following.

  1. Cross out 0s
    1. 10,000/18
  2. Simplify
    1. 5,000/9 (cut in half)
  3. If rounding, get to closest, and add a segment
    1. 5,000/10 = 500
    2. It's a bit less (1/10), so add another 50
    3. = approx 550
  4. If you're not allowed to round, long division

Mental Math

https://www.preplounge.com/en/consulting-forum/mental-math-help-7962

https://www.preplounge.com/en/consulting-forum/is-quick-mental-math-a-skill-that-can-be-learned-5210

Conceptual/Contextual Math

https://www.preplounge.com/en/consulting-forum/materials-for-practicing-conceptual-case-math-8016

https://www.preplounge.com/en/consulting-forum/math-concepts-6951

Key Math Equations

https://www.preplounge.com/en/consulting-forum/math-equations-their-use-7934

Math Practice

https://www.preplounge.com/en/consulting-forum/case-math-practice-6877

Anonymous B
on May 31, 2022
Amazing
Deleted user
edited on Jul 02, 2021

Its not about speed and mental maths. Thats not the point. Obviously you need to show that you are comfortable with numbers.Take some extra seconds to do your calculations. Thats a better outcome than trying to do things quickly and getting the calcs wrong.

5% error margin is okay.

So, for calculations involving large numbers you can apply the following approaches:

  • Increase the number of steps by expanding the numbers e.g 43*78= (40+3)*78= 40*78 + 3*78 = 40*70+ 40*8+ 3*78. Hope you get the point
  • Round up or down and add % error, so in example above you can use 40*80 

So, for a large number divided by 365, its okay to use 350 or 400 but make sure to compensate for the error % or you could expand the numerator in multiples of 365. E.g. 4568/365 = (365*12 + 188)/365 

16
Deleted user
on Jul 02, 2021

It's a deviation of ~4%, so that is fine. You might quickly check in with the interviewer if it's OK to give an approximate number or if they want you to calculate precisely. 

Another trick that might be even easier is to divide by 400 and then add 10%.

15
on Jul 02, 2021
Many thanks for your great inputs! I like your method and will incorporate it.
Similar Questions
Consulting
GMAT/Conceptual Questions in MBB Case Interviews?
on May 16, 2025
Global
8
100+
Top answer by
Anonymous
12
8 Answers
100+ Views
+5
Consulting
McKinsey solve redrock case part - should I round the final answer?
7 hrs ago
Global
4
< 100
Top answer by
Mihir
Coach
50% discount on first session | McKinsey Associate Partner and interviewer | Bulletproof MBB prep
3
4 Answers
< 100 Views
+1
Consulting
Is more Math Drills the way to solve my issue?
on May 02, 2025
Global
7
200+
Top answer by
Mattijs
Coach
Free 15m intro call | First session -50% | Bain| Hiring team | 250+ successful candidates
13
7 Answers
200+ Views
+4
How likely are you to recommend us to a friend or fellow student?
0 = Not likely
10 = Very likely
Thanks for your feedback! Your opinion helps us make PrepLounge even better.