The “Two Coins in a Box” Brainteaser | No BS Job Search Advice Radio

EP 844 Jeff Altman, The Big Game Hunter offers an answer to this clever little brainteaser.

Summary

I have another 1 of those fun interview questions that is designed to trip you up.

A box contains 2 coins. One is a double-headed quarter and the other is an ordinary quarter, heads on one side and tails on the other. You drove 1 of the coins from the box and it is heads. What is the probability that the other side shows heads, also?

The 1st time I thought of an answer, my instinct was to think that there was a 50% probability. I paused and paid more attention to the question. I then realized that that couldn't be possible. Here is why.

When the coin is drawn there are 4 possibilities. There is heads and heads; that is one possibility. And that choice appears twice because there are 2 possibilities with a double headed coin. There is heads and tails and tails and heads.. They are telling you right away that you are seeing heads so that 4th option isn't there (tails and heads).

There are 3 possible alternatives. Both of them involving double heads 1 is a heads and a tail. So the correct answer is that there is a two thirds probability that the other side is also going to be a heads. That's because the 4th 1 was eliminated because you drew heads right away. Right away

Jeff Altman, The Big Game Hunter is a coach who worked as a recruiter for what seems like one hundred years. His work involves life coaching, as well as executive job search coaching and business life coaching. He is the host of “Job Search Radio,” “No BS Job Search Advice Radio,” and his newest show, “No BS Coaching Advice.”

Are you interested in 1:1 coaching or interview coaching from me?  Email me at JeffAltman@TheBigGameHunter.us and put the word, “Coaching” in the subject line.

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