# Case math difficulty level

case math MBB
New answer on Apr 30, 2023
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Hi community,

I've been doing some practice case math (standalone and in practice case interviews) lately and noticed that a good handful of them are quite difficult, i.e., need lots of thinking, long formulas, multiple rows of calculations and exhibits. It takes a long time (10 min or more) to solve one, and most of the time there's always some very fine details that if went unnoticed, the answer would be wrong. I'm just wondering how difficult math is in a real case interview? I have my first round with one of the MBB in about two weeks and I'm concerned that it won't be enough time to get my case math up to par.

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Hi there,

I think this is an interesting question that may be relevant for many people. I would be happy to share my thoughts on it:

• I would highly advise you to reach out to an experienced coach who can provide you with real-life case studies to get a realistic impression of the difficulty of quantitative questions.
• This is especially important because I think that a lot of case studies from business school case books are overly complex when it comes to quantitative questions.

If you would like a more detailed discussion on how to best prepare for your upcoming interviews, please don't hesitate to contact me directly.

Best,

Hagen

I definitely agree with Hagen here. There are some cases in these Bschool casebooks that vest so much effort into convoluting complex quantitative knots that it seems to detract from the main focus of learning and improving in cases more generally.

Hi there,

Q: I've been doing some practice case math. It takes a long time (10 min or more) to solve one. I'm just wondering how difficult math is in a real case interview?

In general a math problem during a case should not require 10+ minutes. The reason it takes so long in your case may be because (i) the drills you are using are particularly difficult or (ii) you need to improve your math skills.

Below you can also find some general math tips:

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In terms of how to approach math during 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 math until you find the final answer
5. Propose next steps on the basis of the results you found

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

1. Use correctly the power of 10. 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 to solve simpler problems. In the previous example, you could get 320*10^7 / 70*10^7
3. Keep good notes. This helps to avoid to forget/misreport 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 main fractions results. You can learn by heart fractions and speed up/simplify the computation - the most useful to know are 1/6 ~ 17%, 1/7 ~ 14%, 1/8 = 12.5%, 1/9 ~ 11%.

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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 asked this suddenly in a case interview.

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

Hope this helps,

Francesco

Hi there,

The level of difficulty during the actual interview is a combination of two things:

Objective level of difficulty:

• Real MBB cases are often much less complex than most preparation cases (such as the “Zero Carbon Mine” case I authored, see link here) as it relates to quant and other dimensions. In other words, don't expect real cases to be any more difficult than the 75th percentile you've encountered in practice cases.

Perceived level of difficulty:

• What makes real cases a lot more challenging during the actual interview is the fact that you are in the actual interview, experiencing high stress levels, nerves, tunnel vision, etc., all of which generally impacts performance. However, the right preparation will allow you to perform regardless.

Considering the above, preparation is key to keep you nerves in check. Here's some recommendations:

What you should do:

• Always look for opportunities to use math purposefully for deriving an insight, even minor ones, which you can either run by the interviewer before setting up an equation and executing (written approach if complex) or do in your head (mental math if simple) and only communicate the result i.e., insight to the interviewer.
• Listen carefully when you’re being asked a direct question, which often comes in two parts and e.g., “How much does company X have to raise their ticket price to break even and how realistic do you think this is?” where candidates commonly miss the second part of the question.
• Be mindful of small details to incorporate in your workflow, some of which are optional e.g., reference to a number that was stated somewhere in the prompt, and some of which are crucial e.g., asterisk* behind the header of a column in a data table, referring to a small footnote containing key information.
• Prioritize precision over speed if the two are at odds with each other, which they generally are for most people, considering that you’re not going to be evaluated based on doing things quickly but doing things right and deriving the right insights (that being said, be as quick as you reasonably can).

What you shouldn't do:

• Miss opportunities to show your skills of deriving meaningful quantitative insights e.g., when presented a data table with various lines of salespeople and two columns: (1) total sales and (2) number of customers, where diving the two yields a single comparable metric i.e., sales per customer.
• Guess or estimate to derive an insight when you could actually do the math, which is a red flag (this is fairly common and either due to carelessness where you don’t see the opportunity or you’re not confident in your abilities and actively avoid quant when the opportunity is staring at you – both is bad).
• Ramble about numbers without getting to the point, which should act as a signifier to stop yourself from talking, think about a way to boil things down, and follow the steps above to get to the point (very typical and the interviewer may or may not nudge you in the right direction).
• Ask the interviewer whether you should calculate something down to the second decimal or simply ballpark the result to save time. Knowing when to do which, and confidently doing so, is a crucial part of the skillset you’re meant to demonstrate i.e., good feeling for numbers in general, including required precision.

Please let me know if this is something you'd like to discuss deeper. Happy to help!

Moritz

(edited)

If you are still struggling and only have 2 weeks left, you simply just don't know what you don't know.

10 minutes is not ok and you are “in trouble”. This isn't to scare you, just to wake you up…don't put that \$40k signing bonus and \$200k salary on the line just because you don't want to spend a bit on a coach.

They can “fix” this for you.

Tips:

1. Setup the problem optimally
3. Practice rote math

What you're describing in terms of math is going to happen in the case.

Hi there,

Difficulty varies a bit by firm, so it's hard to make a general statement here. In case you passed an online assessment for the firm, case Maths is typically not more difficult than those, especially for BCG & Bain.

Feel free to reach out via PM, then I can share some resources with real (retired) MBB cases. This should give you a good sense.

Regards, Andi

Hello,

The answer to your question is definitely going to vary by firm. That being said, in general, the difficult parts of case math involves dealing with awkward numbers, and combining multiple operations. You won't be asked to do more complicated operations than division and multiplication (e.g., calculating an ROI), but it might be framed in a way that would require you to take a few steps to figure out what data you should use, what exact calculations you need to perform, and might involve some awkward large numbers for good measure.

My advice for this would be to practice, practice, practice. When approaching a math question, be sure to ask the interviewer clarifying questions to make sure you understand the task at hand. Set up the calculation (on paper, in your head, or out loud to the interviewer) before you do it to make sure you are on the right path before attempting the numbers. Pinpoint exactly what seem to be the most challenging parts of the math for you personally, and try to target those in your practice.

Best of luck!

Hi there,

Great question!

I would say that difficulty levels of math in case interviews vary depending on the firm and the interviewer. However, as a general rule, math in case interviews is not typically as hard as in the practice cases that you may find online. In fact, it's very rare for interviewers to give you calculations that you wouldn't be able to do on paper with a bit of practice.

Usually, math calculations are a part of the case, but they are not the focus of the case. The focus is on how you structure your approach, what assumptions you make, and how you interpret the results. It's more important to show that you can take the information given, structure a logical framework, and come up with insights rather than to make it through every calculation perfectly.

My advice for you is to focus on building your skills on how to structure your approach and think logically about the problem presented. If you can demonstrate a strong understanding of the key drivers in the case, then that is much more important than getting every calculation right.

Lastly, don't forget that it's okay to make mistakes during the case interview. Interviewers are more interested in seeing how you approach the problem and how you recover from mistakes than seeing a perfect solution.

Best of luck with your upcoming interview!

Cristian

Math in cases is rarely complex. What is complex is to be able to quickly do some mental math and associate it with insights to solve the case at hand.

Even more complex is to think about the formula to solve a specific problem, but even that you can usually do by breaking down a problem into 2-3 parts, and then break down again any of those parts into subparts if necessary. But each of the calculations there should be fairly simple.

An associate with a math major from college told me it was 5th grade math at most, so not academically hard, but possibly need to work on mental math techniques.