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Common Math Traps

Exhibit Math problem
New answer on Dec 01, 2022
7 Answers
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Anonymous A asked on Nov 30, 2022

Hi PrepLounge, I noticed that a lot of cases try to trap candidates by using different denominations for figures (e.g., monthly figures when question is asking for yearly figures). Are there any other common traps one should be aware of? Thank you! 

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Ian
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replied on Dec 01, 2022
#1 BCG coach | MBB | Tier 2 | Digital, Tech, Platinion | 100% personal success rate (8/8) | 95% candidate success rate

Hi there,

There are probably an infinite number! Instead of trying to memorize all the traps, make sure you're trained yourself in just taking the right steps for math:

  1. Figure out what you want to calculate….and why (how it will help)
  2. Setup the overarching logic/equation
  3. Look at the data points you have versus don't have
  4. Write down the equation and write down all units
  5. Double-check to make sure it all makes sense

 

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Rushabh
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replied on Nov 30, 2022
Limited Availability | BCG Expert | Middle East Expert | 100+ Mocks Delivered | IESE & NYU MBA | Ex-KPMG Dxb Consultant

Hello,

Yes, some other traps that come to mind:

1) Using different units when it comes to quantity, e.g. ounce, kg, lb

2) Using different currencies

3) Using 4,000,000 is one place and ‘5M’ in another

4) Hard to read graphs with a lot of data to filter through

A common skill to develop is to have an attention for details and to be very meticulous in your calculations. It often helps to write things down very clearly with the units so that you don't miss anything!

All the best!

Rushabh

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Anonymous replied on Nov 30, 2022

Hi there,

Adding to what Rushabh has written, I can also add these two traps/tricks with math.

1- Sometimes the data available is not enough for you to reach to the final answer, yet you try to figure out what you can do with the available data. Or you may come up with assumptions, which may not necessarily be calculation friendly. Asking for a piece of data can make your life much easier.

2- You reach an answer but as long as you do not compare it to some other reference data, you might interpret this quantitative piece of information in the wrong way. A cost item that is a couple of tens of millions of dollars may be only a very small portion of the whole cost structure.

If you fall into any traps while doing a case, I'd suggest giving the same case to any other case partner and observing their behaviors. Do they get it right the first time or do they realize their mistake and correct it after a short while? Or do they just move on with the wrong answer?

Good luck!

Emre

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Emily
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updated an answer on Nov 30, 2022
Ex McKinsey EM & interviewer (5 yrs) USA & UK| Coached / interviewed 300 +|Free 15 min intro| Stanford MBA|Non-trad

Things to listen out for / look out for:

  1. Differences in units (eg monthly / annually; per customer / per segment)
  2. Profit vs revenue
  3. Percent difference - what is it a percent of?

Good luck! 

(edited)

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Dennis
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replied on Nov 30, 2022
Ex-Roland Berger|Project Manager and Recruiter|7+ years of consulting experience in USA and Europe

A lot of candidates tend to forget to differentiate between total market and addressable market when dealing with market shares during cases

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Mario
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replied on Nov 30, 2022
Ex-Mckinsey (analyst->associate->manager) and now in tech (Bytedance) + Part time interview coach and mentor

Hi there,

 

Typically it's mostly units, zeros (using 000 instead of symbols like K,M,B), and timeframes that cause the most mistakes.

 

Mario

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Pedro
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replied on Dec 01, 2022
30% off in April 2024 | Bain | EY-Parthenon | Roland Berger | Market Sizing | DARDEN MBA

Good answer above. Just wanted to highlight that these are not really traps. It's just real-life complexity.

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Ian gave the best answer

Ian

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