Best Casebook to Practice Math Structuring

case math
New answer on Feb 01, 2021
8 Answers
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Anonymous A asked on Jan 30, 2021

Hello

I am having issues structuring the math formulas (e.g. what to do given a both of numbers) and was wondering if anyone has recommendations for good case books to go through specifically for the math component?

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Ian
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replied on Jan 31, 2021
MBB | 100% personal interview success rate (8/8) and 95% candidate success rate | Personalized interview prep

Hi there,

Most casebooks have a section on math...but I wouldn't rely on this for your prep.

  1. 100% Recommend Rocket Blocks. https://www.rocketblocks.me/
  2. Online "Drills": https://www.jetpunk.com/quizzes/fast-math-multiplication-quiz
  3. Math sheets (print these and do them on paper): https://www.math-drills.com/
  4. In addition to that, you can ask other PrepLoungers to case you on math-heavy cases. You can also search for those case types here and work through them yourself.

Some key formulas/concepts:

  • Breakeven
  • NPV (with + without growth, perpituity + 1-2 years from now)
  • % Change
  • ROI
  • Margin
  • Markup
  • Inventory turnover

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Some great answers from a variety of angles have already been asked. Check these out!

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

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Gaurav
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replied on Jan 31, 2021
Ex-Mckinsey|Certified Career Coach |Placed 500+ candidates at MBB & other consultancies

Hi there!

I would recommend you to use:

1) PrepLounge´s Mental Math Tool - https://www.preplounge.com/en/mental-math.php
2) Books for the GMAT preparation, especially pay attention to the Integrated Reasoning section
3) McKinsey PST
4) Take a session with a career coach to improve your math structuring and case solving overall

Hope it helps!

All the best,
GB

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Francesco
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replied on Jan 31, 2021
#1 Coach for Sessions (4.000+) | 1.500+ 5-Star Reviews | Proven Success (➡ InterviewOffers.com) | Ex BCG | 9Y+ Coaching

Hi there,

I personally like INSEAD as casebook – including for math problems.

In terms of how to approach math in the case, this is what I would recommend:

  1. Repeat the question – sometimes candidates do mistakes answering the wrong question
  2. Ask for time and present how you would like to proceed from a theoretical point of view
  3. Perform the math and present the interim steps to keep the interviewer aligned – don’t just say the final number
  4. Continue with the computations until you find the final answer
  5. Propose next steps on the basis of the results you found

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

  1. Use correctly 10^ powers in your math computation. For example 3.2B/723M can be transformed in 3200*10^6/732*10^6, which makes it easier to deal with math
  2. Ask if it is fine to approximate. When you have to deal with math in market sizing - and sometimes even in business cases - you are allowed to approximate math to simplify the computation. In the previous example you could transform the computation in 320*10^7/70*10^7
  3. Keep good notes. One of the reasons people do mistakes with big numbers is that they don't keep their notes in order and forget/misreport numbers
  4. Divide complex math in logical steps. This is something you can use for big numbers after the application of the 10^ power mentioned above. For example: (96*39)*10^6 à 96*40 - 96*1 = 100*40 - 4*40 - 96*1 = 4000 – 160 – 100 + 4 = 3744*10^6
  5. Use shortcuts for fractions. You can learn by heart fractions and thus speed up/simplify the computation - the most useful to know are 1/6, 1/7, 1/8, 1/9.

I would also recommend to practice math under pressure - not just math. Many candidates are totally fine doing 67% of 67 in normal conditions, but freeze if you ask this suddenly in a case interview.

In order to do so, try always to use a timer with a strict time constraint when you practice math – this will create pressure and help to replicate the actual conditions of the interview.

Hope this helps,

Francesco

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Florian
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replied on Jan 31, 2021
#1 rated McKinsey Coach | Top MBB Coach | 5 years @ McKinsey | Author of the 1% | 120+ McK offers in 18 months

Hey there,

80% of interviewees struggle with case math. Hence, it should always become a big focus of your interview preparation.

My approach to case math question would be the following:

  1. Listen. Carefully and actively listen to what your interviewer tells you
  2. Clarify. Before you dig into the quantitative problem at hand, slow down: clarify the objective and numbers you heard from the interviewer or extracted from charts or data tables. This is especially important in the era of Zoom calls.
  3. Draft your logic. Set up your planned approach to the calculation while asking for some time. Draft your logic on the piece of paper you have been handed by the interviewer
  4. Communicate your approach. Lead the interviewer through your approach. This way you’ll make sure that mistakes are spotted early
  5. Calculate. When the interviewer agrees with your approach, follow through with the calculations – alone and in peace. Again, ask for some time and use the paper
  6. Sanity check your results. Make sure there are no mistakes in your calculations. Do the numbers make sense?
  7. Communicate your results top-down. Summarize the result(s) you got in a confident and assertive manner - top-down communication!
  8. Come up with a hypothesis. When you get a final result, DON’T STOP THERE. Quickly explain and interpret the numbers. Relate the numbers to the problem at hand. Remember why you set up the calculation in the first place. It is important to discuss the ‘so what’ of your quantitative analysis.

I have written a very detailed and long (free) article on case math here and also developed a math video academy with 25 tutorials and a prep book with almost 2,000 practice exercises (which is key to train and prime your brain to come up with math questions):

https://strategycase.com/case-interview-math-the-ultimate-guide

Cheers,
Florian

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Ken
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replied on Jan 31, 2021
Ex-McKinsey final round interviewer | Executive Coach

In addition to Ian's suggestions, the McKinsey Problem Solving Test (https://www.mckinsey.com/careers/interviewing) is another great source to practice the underlying quantitive skills behind a case including structuring, exhibit reading, back-of-the-envelope math). It's no longer commonly used as part of the selection process but I still believe it's a terrific resource for practicing!

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Clara
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replied on Jan 31, 2021
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut

Hello!

To add on top of what has been shared before, I would practice with GMAT.

There are free exams in the internet that you can use for practice (the one of LBS MBA page, Verits prep, as well as some free trials for courses such as the one of The Economist (https://gmat.economist.com/)

Hope it helps!

Cheers,

Clara

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Henning
Expert
replied on Jan 31, 2021
Bain | passed >15 MBB interviews as a candidate

All the GMAT prep materials work great. In addition, Rocketblocks is a great resource for all of these case interview skils you need to prepare for.

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Antonello
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Content Creator
replied on Feb 01, 2021
McKinsey | MBA professor for consulting interviews

Hi,

In addition to the casebooks suggested, in interviews the aspect which causes more errors is pressure: start to solve calculations with strict time constraint. For longer formulas always share the calculation structure with interviewer before starting to write down the numbers: this helps to take time, to reduce the pressure and gives you the opportunity to receive a first feedback by the interviewer avoiding wrong calculations.

I recommend practicing with:

Best,
Antonello

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Ian gave the best answer

Ian

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