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Ian

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291 Meetings

25,088 Q&A Upvotes

USD 289 / Coaching

7

Math part in Cases

Hi together,

I am ok in most parts of the cases. However in the math part, I always get the problem wrong or generally dont understand the math problem. Where can I practice those or do you have any tips how I should prepare them?

Thank you!

Hi together,

I am ok in most parts of the cases. However in the math part, I always get the problem wrong or generally dont understand the math problem. Where can I practice those or do you have any tips how I should prepare them?

Thank you!

7 answers

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Book a coaching with Ian

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Hi Alina,

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

----------------------------------------------------------------------------------

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

Hi Alina,

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

----------------------------------------------------------------------------------

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

Book a coaching with Francesco

100% Recommendation Rate

3,465 Meetings

16,860 Q&A Upvotes

USD 449 / Coaching

Hi Alina,

Have you practiced the math part for actual cases? If not, doing the math part only using some good casebooks (eg INSEAD) would be a good starting point.

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 based on 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

Hi Alina,

Have you practiced the math part for actual cases? If not, doing the math part only using some good casebooks (eg INSEAD) would be a good starting point.

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 based on 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

Book a coaching with Florian

100% Recommendation Rate

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USD 219 / Coaching

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

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

Book a coaching with Clara

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USD 229 / Coaching

Hello Alina,

There are two big workstreams when it comes to the math part of a case:

  • Math calculations and algebra:
    • Practice is here your best friend. From basic algebra to fractions and ratios, you need to gain speed. It also helps to get comfortable with scientific notation.
  • Understanding the problem and being able to translate the words into numbers:
    • This part is trickier, since it´s not that easy to practice. I would strongly recomment you practice it with the Integrated Reasoning part of the GMAT exam.
    • 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/)
    • Furthermore, you can leverage the MBB tests (https://www.myconsultingoffer.org/case-study-interview-prep/bcg-online/, https://www.psychometricinstitute.co.uk/Free-Aptitude-Tests.asp, and many others)

Hope it helps!

Cheers,

Clara

Hello Alina,

There are two big workstreams when it comes to the math part of a case:

  • Math calculations and algebra:
    • Practice is here your best friend. From basic algebra to fractions and ratios, you need to gain speed. It also helps to get comfortable with scientific notation.
  • Understanding the problem and being able to translate the words into numbers:
    • This part is trickier, since it´s not that easy to practice. I would strongly recomment you practice it with the Integrated Reasoning part of the GMAT exam.
    • 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/)
    • Furthermore, you can leverage the MBB tests (https://www.myconsultingoffer.org/case-study-interview-prep/bcg-online/, https://www.psychometricinstitute.co.uk/Free-Aptitude-Tests.asp, and many others)

Hope it helps!

Cheers,

Clara

Book a coaching with Gaurav

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USD 239 / Coaching

Hi Alina,

Here is a math app for practicing math fractions and percentages from one of PL participant https://apps.apple.com/us/app/case-math/id1507653375?mt=8&ign-mpt=uo%3D4

Here is a tool provided by PrepLounge https://www.preplounge.com/en/mental-math.php

For practicing and improving your math you can find also some apps and tools, besides Victor Cheng’s math tool (Magoosh's mental maths app, Mental math cards challenge app, etc). But there are some facts that will help in overall improvements:

  • Consulting math is very different from academic math. Working consultants - and consulting interview candidates - are always under time pressure. Results are what matter and answers are required simply to be good enough to guide business decisions, rather than being absolutely correct. The next important thing is that rather make it on the paper to structure the notes and then to communicate the results clearly rather than make your calculations fast
  • The time pressure in case interviews is severe and you cannot afford to waste time. But to make your calculations right you shouldn’t be in a rush. So, I would recommend you here to work on both - practice with time limitations and learn how to keep your mind peaceful and concentrated (it might be not so popular advice here, but mediations really make their job here ). Be comfortable and confident to state your answers, not as a question. Interviewers notice this, and this will not give credit. If you need any further help or career advice, feel free to reach out.

Hope it helps!

Cheers,

GB

Hi Alina,

Here is a math app for practicing math fractions and percentages from one of PL participant https://apps.apple.com/us/app/case-math/id1507653375?mt=8&ign-mpt=uo%3D4

Here is a tool provided by PrepLounge https://www.preplounge.com/en/mental-math.php

For practicing and improving your math you can find also some apps and tools, besides Victor Cheng’s math tool (Magoosh's mental maths app, Mental math cards challenge app, etc). But there are some facts that will help in overall improvements:

  • Consulting math is very different from academic math. Working consultants - and consulting interview candidates - are always under time pressure. Results are what matter and answers are required simply to be good enough to guide business decisions, rather than being absolutely correct. The next important thing is that rather make it on the paper to structure the notes and then to communicate the results clearly rather than make your calculations fast
  • The time pressure in case interviews is severe and you cannot afford to waste time. But to make your calculations right you shouldn’t be in a rush. So, I would recommend you here to work on both - practice with time limitations and learn how to keep your mind peaceful and concentrated (it might be not so popular advice here, but mediations really make their job here ). Be comfortable and confident to state your answers, not as a question. Interviewers notice this, and this will not give credit. If you need any further help or career advice, feel free to reach out.

Hope it helps!

Cheers,

GB

Book a coaching with Henning

100% Recommendation Rate

182 Meetings

5,481 Q&A Upvotes

USD 189 / Coaching

  1. Take some time at the beginning to structure the problem. Define the question clearly (in this case: What do you want to calculate, using the data you have).
  2. Then develop a framework (the equation) and take the interviewer along by telling them what you will calculate. In a face-to-face meeting, you can show them the equation to take them along, through zoom you need to overinvest in this stage. End with the question on whether this makes sense or the interview would have any comments.
  3. Once aligned on the equation, execute the math. During the execution, pay attention to potential short-cuts. Often you don't need to make the complex written division if you see a short cut. Confirm with the interviewer if it's OK to make simplifications (e.g. calculating with +-5% accuracy, multiplying with 100 instead of 97, etc), rather than calculating the last digit. If you are insecure about your mental and written math skills and about seeing these shortcuts, there are many resources on practicing this. GMAT resources are a good start.
  4. Before you communicate your results, do a quick mental sense check. Is the number in the right ballpark, or does it feel completely out of whack? If it feels wrong, tell the interviewer about your result, but that it doesn't feel right so you want to double-check for potential sources of error.
  5. Communicate your results and give the interviewer the chance to react before using it in your next steps.

If you want to practice the execution specifically, there are tools here on preplounge and other platforms like Rocketblocks.

  1. Take some time at the beginning to structure the problem. Define the question clearly (in this case: What do you want to calculate, using the data you have).
  2. Then develop a framework (the equation) and take the interviewer along by telling them what you will calculate. In a face-to-face meeting, you can show them the equation to take them along, through zoom you need to overinvest in this stage. End with the question on whether this makes sense or the interview would have any comments.
  3. Once aligned on the equation, execute the math. During the execution, pay attention to potential short-cuts. Often you don't need to make the complex written division if you see a short cut. Confirm with the interviewer if it's OK to make simplifications (e.g. calculating with +-5% accuracy, multiplying with 100 instead of 97, etc), rather than calculating the last digit. If you are insecure about your mental and written math skills and about seeing these shortcuts, there are many resources on practicing this. GMAT resources are a good start.
  4. Before you communicate your results, do a quick mental sense check. Is the number in the right ballpark, or does it feel completely out of whack? If it feels wrong, tell the interviewer about your result, but that it doesn't feel right so you want to double-check for potential sources of error.
  5. Communicate your results and give the interviewer the chance to react before using it in your next steps.

If you want to practice the execution specifically, there are tools here on preplounge and other platforms like Rocketblocks.

Book a coaching with Antonello

98% Recommendation Rate

165 Meetings

6,604 Q&A Upvotes

USD 219 / Coaching

Hi Alina,

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

Hi Alina,

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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