I am good at calculating math, but I have trouble setting up the math correctly.

Question

Hi everyone at Preplounge,

I need help - I have come to the conclusion that I am good at math but I often times fail to get that math set up correctly. I have been doing a lot of cases off of case coach and have realized that there are math setups that are not just the regular “break even”, “ROI”, “payback period” equations.

For example, there was an instance I had to do NPV and PV of items. I have been through one round of McKinsey interviews and found that the math was not that complicated at all. Should I expect the math to be confusing/tricky in other interviews with MBB firms - and how can I practice my math setup? I've noticed there are a lot of mental math tools online but not math setup help.

Thank you community!

Answer 1

Hi there,

How to structure math in a case

Have a seperate "math" scrap sheet of paper
Grab a new sheet of paper every time you're entering a new phase of the case...number and title it
Use tables to organize numbers
Write out the equation before doing the math
Never forget to write down units
Circle key numbers AND write down the "so what"

How to practice math

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

100% Recommend Rocket Blocks
Online "Drills": (Sites like JetPunk and Preplounge)
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 math 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

Answer 2

Great question.

For non-complex or complex equationsn alike, I always like to:

Map out all the variables
If more than two or three different inputs / outputs you are solving for, share aloud with your interviewer that you are looking to solve for “X, and Y” considering “A,B,C." Validate that your understanding is correct.
Once validated, lay out the equation internally and once you have it on paper, share once again with your interviewer (there could be a few steps if solving for more than one variable, for example).
If for some reason you get a question that can be tricky to solve, such as an NPV, share with your interviewer some short-cuts that you plan on taking and validate that those are OK with the interviewer before proceeding
Once variables and later equations validated, periodically update your interviewer on your progress (no need to impress and solve each step of the question aloud - this leads oftentimes to silly mistakes)

Do not know if this perfectly responds your question. Happy to discuss more.

Best,

Daniel.

Answer 3

Hey there,

Indeed, McKinsey math is usually not that complicated, yet its still the biggest rejection driver in my opinion since you need to solve every case math problem swiftly and accurately, consistently over multiple cases (all under stress).

How can you practice:

1. Get good university case books. Google or PM me

2. Break math problems down into individual steps, not formulas. Look for simplification opportunities (esp. at McKinsey)

3. Work through as many math problems as you can (focus only on setting up the approach if your computations are fine to save time)

4. Create an error log, spotting what types of problems you are struggling with most. You will a. not make these mistakes again, b. know where to focus your preparation more

5. Learn how to communicate your approach properly to the interviewer (break it down into small steps, present every step)

Bonus point: Don't stop at the calculation, answer the question, interpret it in the context of the case, then discuss the next steps and the way forward

Alternatively, I also created a successful case math program with 20+ videos and 2,000 practice examples that I can offer in combination with my coaching.

Cheers,

Florian

Answer 4

Hello!

You are raising an excellent point, and I totally agree: the math you see in some of the published cases is much more complicated and sophisticated that the one you find in cases.

I would find it hard to believe that you need to an NPV calculation dividing by 1+r and the required calculations in an MBB interview.

Is more aobut agility, overal order of magnitude, etc.

Hope it helps!

Cheers,

Clara