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Market Sizing questions (or Brainteasers) make for a great way to start your case interview practice. This Oliver Wyman case will get you started.


You step into an elevator on the ground floor and there are 30 floors above you. Another person steps into the elevator with you.

What is the probability that the other person in the elevator will get out on the same floor as you?

Assume two people stepped into the elevator with you. What is the probability that both are getting out on the same floor as you?


In this fun Brainteaser / Market Sizing Question, you’re being asked a creative question meant to test both your analytical and creative thinking processes. Brainteasers are solved the same way you solve a Market Sizing question – by breaking down the solution into component parts.

There are 2 approaches you can take: either top-down or bottom-up. Which will help you best solve the problem?

The 4 steps for solving Market Sizing problems:

  1. Structure your approach (5+ steps is ideal)
  2. Make assumptions
  3. Do the calculations
  4. Get to an insight

You could expect a question like this in a round 0 interview / initial phone screen, or find it incorporated into another case in your interviews (e.g. an M&A case).

Oliver Wyman Group Interview Tips

Oliver Wyman is looking for sharp analytical skills in its case interview candidates. This is an excellent case that will test those skills.

To make the most of your case interview practice, focus on finding 1 area of improvement in this case.

If you need more resources in your case interview practice, book an hour with an ex-MBB coach now.

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