[klenwell]

I used to bring this question with me to interviews in my back pocket, so to speak:

Two people, Alice and Bob, are each flipping a coin repeatedly. Alice will stop when she flips two heads in a row (HH). Bob will stop when he flips a head followed immediately by a tail (HT).

Who will flip the coin more times on average: Alice, Bob, or is there no difference?

I had come across it on Metafilter a few years ago:

https://www.metafilter.com/147228/You-blew-it-and-you-blew-i...

I figured if I ever got a whiteboard or coding problem where I was completely lost, I might try saying something like, "I have no idea how to solve this. But here's a fun problem I came across recently that we could work on together."

There were a couple times where I got a question I couldn't solve. But I never had the courage to pull out my backup problem.

[dekhn]

Discussed here: https://news.ycombinator.com/item?id=11282480 And https://www.quantamagazine.org/mathematicians-discover-prime...

If the interviewee gets stuck just have them write a program and spit out the values averaged over many runs. This is what convinces a lot of people about the Monty Hall problem too

[EForEndeavour]

I admire your preparation of a fallback brainteaser to throw back at the interviewers in case you ever get flummoxed, but I feel it would take some real storytelling skills or charm to "sell" this as anything but a desperate attempt at a switcheroo. (Maybe the fact that I'm so pessimistic about this tactic means I'm the kind of person who would definitely fail miserably if I ever tried it.)