Approach to solve Math in case interview

Hey Anonymous!

Thanks for sharing your difficulties, it's always a great first step! First of all, no worries: you are not alone, at least 20% of my coachees have the same 'blank panic' for exhibits and maths.

If I understand correctly, you are talking about two different things in the first question. Let me give you my two cents on where to start.

Graph/Exhibit Analysis

• Your approach is generally correct, but it's very general and does not guarantee you'll be able to communicate something useful/insightful for the case :)
• The Exhibit Analysis should be considered as a test of your data-to-business translation skills: candidates that focus too long on understanding, framing, or explaining the data tend to dedicate fewer seconds to extracting actionable business insights -- missing the main purpose of this case section!
• My personal advice: rather than starting from the "process"/comms structure, you should start with a few drills where you learn how to extract non-obvious insights from the exhibit. Everything will be much easier once you build that mental muscle!

Maths

For Math, I advice my Novice coachees to start (for the first 3-5 cases) to follow a more cadenced approach. Try to divide your content and comms in three steps:

• First, try to align on the quantitative logic with your interviewer as if we were communicating this to the CFO of the company during an elevator ride. E.g.: "To determine if this new product launch is viable, we want to obtain the incremental profit margin. We first need to calculate the incremental contribution margin per unit, multiply it by the forecasted volume (adjusting for any cannibalization of our existing products), and then subtract the fixed launch costs like marketing and R&D. Does this approach sound reasonable?"
• Second, convert the logic to an equation, using variables. 
  E.g.: "The equation will be: Incremental Profit = [ (Price - Variable Cost) * Quantity * (1 - Cannibalization Rate) ] - Fixed Costs"
• Third, plug numbers in your equation and start calculating
  E.g.: "Plugging in our data: we have a Price of $100 and Variable Costs of $40, giving us a $60 margin. With an expected Volume of 10,000 units and a 10% cannibalization rate, our gross incremental margin is $540,000. After subtracting the $200,000 in fixed costs, the project yields a net positive impact of $340,000."

After a few cases, you'll improve and be able to compress these steps -- but imho it shouldn't be your focus right now

Of course, I'd love to help you! Feel free to DM me for a quick intro call :)

Best,

Tom

Hi, 
here is how I would recommend you to approach the math issue.

1. Define clearly what you are calculating: Always start by stating exactly what you are trying to compute and say it aloud For example if you are asked to estimate the tire market in the USA you will specify: “I am going to estimate the tire market for cars only in the US, including both OEM and replacement segments".  This will ensure you and the interviewer are aligned on scope.
2. Take a moment to think: Once the scope is confirmed pause  to structure your approach.
3. Start from the question, not the data: Ask yourself how would I calculate this in an ideal world? What inputs do I need?Write the formula in words; (no numbers yet!)
4. Map the data to your structure: Check what data you have and how it fits  your formula.If something is missing, ask for it.
5. Only then move to numbers. Now you can plug numbers into your formula
6. Now you have your structure ready and you can communicate it to hte interviewer. Play back your approach before  doing any math, explain your formula in plain words (still no numbers!). Get a clear green light from the interviewer.
7. Once aligned, perform the math step by step.
    

Hope this helps
Franco

Hello there,

Let me just start by saying that you're not alone - most candidates I coach face some difficulty with the quantitative questions and that requires a bit of practicing to overcome. Good news is that this is definitely coachable, bad news is that it requires some effort on your part in addition to getting the coaching you need.

My recommendation for approach is as follows:

1. Understand the question and underlying data provided:

This step ensures that you know what you are solving for, what is being asked, you validate all the numbers you were given and ensure that you captured it correctly. This might even require some discussion with the interviewer in order to confirm your understanding of all the given. This step does not involve stepping into solution mode

2. Come up with a step-by-step approach to solving the question

With the question asked clear in you mind, you need to figure out what drives the solution, and come up with high-level step-by-step approach to reaching the answer by explaining what step 1 is, step 2, and so on until step n. In this step you do not do calculations, you do not mention numbers, but focus mainly on the approach. You start your answer by explaining this methodology and ensuring the interviewer is aligned

3. Solve for the answer

Having clear steps lined up enables you now to focus on the calculations. Move from each step to the following one, reflecting on the intermediate results as you calculate them. Simplify complex math equations by breaking them down into simpler manageable chunks

4. End with recommendation and reflections

Coming up with the answer is not the end of the story for the consultant. You now need to communicate your findings in top-down fashion explain any risks or next steps that need to be taken to support the client given the case objectives

I hope the above is helpful and happy to connect if you need more support.

Regards,

Sherif

P.S. This content is not generated with AI and is based on my experience with 350+ interviews with McKinsey and over 500 coaching sessions with aspiring candidates

For quant questions in cases, I’d keep it structured and explicit:

1) Clarify the goal + list what’s given
Be very clear on what you’re solving for, and write down all available data.

2) Build the equation first
Start with the formula based on the goal, then plug in the numbers you already have.

3) Address the gaps
For any missing variables, either ask for the data or validated reasonable assumptions.

4) Walk through the math out loud
Explain each step as you go so the interviewer can follow your thinking.

For example, if you’re calculating profit:
Profit = Revenue – Cost
Revenue = Price × Volume

You might say: “Price is X and volume is Y per day. Assuming these are representative averages, I’ll annualize by multiplying by 365.”

It can feel very unnatural at first, but this level of structure is exactly what interviewers are looking for.

If helpful, I’m happy to walk you through this step-by-step on a free intro call. Feel free to DM me. 

Hi there,

Math Setup

• Have a separate "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"

Regarding Improving Fast Math Skills

• Math sheets (print these and do them on paper): Math Drills
• Leverage the free PrepLounge resource: preplounge.com/en/mental-math.php
• Rocketblocks is great for math in the context of a case: rocketblocks.me

Regarding Improving Anxiety

1. Practice, practice, practice ... just like playing an instrument, practice until it becomes second nature... then when you perform in front of an audience, muscle memory takes over from stage fright!
2. Practice with people who make you nervous ... don't keep casing yourself or casing with other PrepLoungers! You need to feel as nervous when practicing as you will in the real thing. To do so, you can do any (or all) of the following:
   • Ask for a buddy/case partner from target firms to which you're applying
   • Ask anyone you have a relationship with at your target firms to give you a practice case
   • Ask your school's career office to give you a case
   • Ask a coach to give you a case (and ask them to be tough/strict/non-friendly)
   • Still ask PrepLoungers to case you, but ask them to jump straight into it without conversation beforehand (i.e. simulate the real thing)
   • Change your environment ... instead of casing at home, go to a library or office room. Changing the scenery may trigger you to be less relaxed
3. Practice with the unknown ... ask people to give you "weird" cases. Ask people to throw everything they have at you (curveballs, confusing statements, etc.)... you'll get comfortable with tripping up (and recovering)
4. Practice fast math

Mental Math Q&As: Is quick mental math a skill that can be learned? | Mental math help

Interview Anxiety: Tips on interview anxiety

Both problems are fixable.

On building the formula: the blank mind happens because you are doing too many things at once. Break it into three steps.

First, restate what you are being asked to calculate before you look at the data. Ten seconds. Stops you going in the wrong direction.

Second, label what you have. Look at the data and understand what each number represents. Do not use it yet.

Third, connect them. What formula links what you have to what you need? Most case math comes down to a few basics. Revenue is price times volume. Profit is revenue minus cost.

On communicating: say what you are doing before you do it. Something like: I am going to find annual profit by calculating total revenue first, then subtracting costs. Interviewers are watching how you think, not just checking the answer.

Practise the math portion on its own before your next case. Not full cases. Just the math, until the three steps feel automatic.

Hi there,

It's a bit more complicated than that. And I can't give you a genuinely useful answer in the confines of a Q&A section. 

First, I would differentiate between calculation questions and chart interpretation. 

If you're most interested in the latter, I recommend you

First, read the exhibit with the interviewer and clarify anything that doesn't make sense

Then, take time and come up with 2-4 insights

Then, communicate the insights in a structured manner, for each starting with a data point, explaining what it means and what the client should do as a consequence of it

Then, connect the dots between the different insights.

If you want help on this reach out and I can take you through several examples. 

Best,
Cristian