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Killer Interview Questions

Following a warm response to the last brainteasing blog, I thought I’d share some more outlandish interview questions.

However, unable to agree on a perfect answer for another McKinsey corker (“How many golf balls are in the air over the US…[snaps fingers]….now”), we’ve gone for something a little more straightforward.

Question

You are on a game show. There are three doors in front of you, labelled A, B and C. The host tells you that behind two of them he has hidden a goat, and behind one of them a car.

Now choose a door.

Before the host reveals your prize, he opens one of the other two remaining doors to show a goat. He asks if you’d like to stick to your original choice, or switch to the other unopened door.

Should you stick or switch?

Answer

Uncomfortably counter-intuitive though it is – switching doubles your chances of winning. The reason hangs on the fact that the host knows which doors are which, and deliberately chooses to reveal a goat – thereby skewing the probabilities so that it is not a 50:50 split. The simplest way of thinking about it is this: The only situation in which switching is a losing strategy is if you chose the car to begin with (1/3). If you chose either of the goats to begin with (2/3), then switching will win. Several alternative explanations can be found here.

Jay Scott is a consultant on the FreshMinds Talent Interim team