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Math practice

Case Calculations Mental Maths
New answer on Nov 10, 2023
7 Answers
458 Views
Anonymous A asked on Nov 05, 2023

Good morning everyone! I would like to ask your kind recommendations on materials/website I can improve my calculation skills. I can structure the estimation fairly well, however but embarrassingly, I often make calculation mistakes if it involves decimals and not easy numbers (such as 0.37 * 77) I can get by if I'm allowed to round it, but sometimes rounding doesn't really make sense, and I often make a mistake. I can do it if I'm calm but if the case involves multiple calculations like above, I make mistakes…

If anyone had the same issue and managed to fix it, I'd appreciate if you can share some good materials/website to practice!

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Moritz
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updated an answer on Nov 06, 2023
ex-McKinsey EM & Interviewer | 7/8 offer rate for 4+ sessions | 90min sessions with FREE exercises & videos

Hi there,

A very common problem among candidates, which is relatively easy to train. Here's some thoughts on the matter:

  1. The mental math tool on Preplounge is great. Also, Rocketblocks is pretty good for quant. Get access to these tools asap and use them whenever you can e.g., to wind down after a long day of case cracking…
  2. Write down random numbers on a sheet of paper with different operators and start practicing! You can make it complex with lots of numbers, operators, maybe even a variable to solve for, etc. Nothing beats practice, and if you're far from where you need to be, you need plenty of practice! Also, using paper will serve you well in the interviews, where you will working paper based.
  3. Arithmetic i.e., execution, is just one of the steps you need to get right for a great quant score. There's generally more steps that you shouldn't neglect (but lots of candidates do…), breaking down into the following:
    1. Identifying opportunities to do math when you're not specifically being asked e.g., you get an excibit with lots of numbers. Do you have the drive to crunch some numbers to device some non-obvious insights or are you just going to talk all day about all those numbers without calculating anything?
    2. Setting up an equation is something you have to learn, whether math is self-prompted or when you're being asked a specific question. This can often include solving for a variable x, so you need to get comfortable with longer equations and unknowns.
    3. Doing arithmetic, as described above, is the execution part and just one step in a sequence that you have to get right to show great quant skills.
    4. Contextualizing the result is not necessarily a quant skills and falls more in the conceptual skills domain, but it something that you absolutely have to get right! There's nothing worse than an interviewee giving me a number like I'm a teacher doing a math test. You need to use the output to inform either the next step or a certain insight.

Hope this helps a bit. Best of luck!

Moritz

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Francesco
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replied on Nov 05, 2023
#1 Coach for Sessions (4.500+) | 1.500+ 5-Star Reviews | Proven Success (➡ interviewoffers.com) | Ex BCG | 10Y+ Coaching

Hi there,

Q: I would like to ask your kind recommendations on materials/website I can improve my calculation skills.

In terms of general math tips, I would recommend the following:

  1. Use the power of 10 correctly. For example, 3.2B / 723M can be written as 3200*10^6 / 732*10^6.
  2. Ask if it is fine to approximate. You can ask the interviewer if you can approximate complex math. If allowed, this will help solve simpler problems. In the previous example, you could get 320*10^7 / 70*10^7. 
  3. Keep good notes. This helps to avoid forgetting or misreporting numbers. 
  4. Divide complex math into multiple simpler steps. For example: (96*39)*10^6 → 96*40 - 96*1 = 100*40 - 4*40 - 96*1 = 4000 – 160 – 100 + 4 → 3744*10^6.
  5. Learn the main fractions results. You can learn by heart fractions and speed up or simplify the computation - the most useful to know are 1/6 ~ 17%, 1/7 ~ 14%, 1/8 = 12.5%, 1/9 ~ 11%.

Hope this helps,

Francesco

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Alberto
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replied on Nov 06, 2023
Ex-McKinsey Associate Partner | +15 years in consulting | +200 McKinsey 1st & 2nd round interviews

Hi there,

Some materials to improve your maths:

Don't forget to also practice under time pressure.

Best,

Alberto

Check out my latest case based on a real MBB interview: Sierra Springs

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Cristian
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Content Creator
replied on Nov 07, 2023
#1 rated MBB & McKinsey Coach

Hi!

Feel free to reach out and I can share the guide that synthesizes the methodology I also use with my candidates for calculations.

Good luck!
Cristian

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Practicing for interviews? Check out my latest case based on a first-round MBB interview >>> CodeWave  

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Ian
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Content Creator
replied on Nov 07, 2023
#1 BCG coach | MBB | Tier 2 | Digital, Tech, Platinion | 100% personal success rate (8/8) | 95% candidate success rate

Hi there,

I love mathdrills dot com. Print out the sheets across multiplication, division, etc. and just rote practice with those sheets every day.

Then, apply that via rocketblocks.

Finally, apply via cases.

Also, learn the key techniques for math (splitting technique, halving/doubling technique, rounding technique etc.) to make the math much easier!

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Nikita
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replied on Nov 06, 2023
MBB & Tier2 preparation | 85+ offers | 7 years coaching | 2000+ sessions | PDF reviews attached

Hey,

Hire a math tutor (non necessarily with a consulting background) to help you with your sticking points. Oftentimes even a few sessions can make a difference.

I took sessions with a math tutor when preparing for consulting interviews myself and now I teach some of those math concepts to my own students.

Good luck!
Nick


 

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Frederic
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replied on Nov 10, 2023
ex Jr. Partner McKinsey |Senior Interviewer| Real Feedback & Free Homework between sessions|Harvard Coach|10+ Experience

Just adding another ressource: Khan Academy

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Moritz gave the best answer

Moritz

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