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

case math Math problem
New answer on Jul 02, 2021
3 Answers
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Anonymous A asked on Jul 02, 2021

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

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Ian
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updated an answer on Jul 02, 2021
MBB | 100% personal interview success rate (8/8) and 95% candidate success rate | Personalized interview prep

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

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

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(edited)

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Anonymous B on May 31, 2022

Amazing

Adi
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updated an answer on Jul 02, 2021
Accenture, Deloitte | Precision Case Prep | Experienced Interviewer & Career Coach | 15 years professional experience

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 

(edited)

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Henning
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replied on Jul 02, 2021
Bain | passed >15 MBB interviews as a candidate

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%.

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Catrina on Jul 02, 2021

Many thanks for your great inputs! I like your method and will incorporate it.

Ian gave the best answer

Ian

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