I've used a similar question, but with two coins. I think if I am ever in a position where I am hiring again, I may follow-up that question with this extension to 100 coins.

What is the most common answer? Typically, I get either blank stares or a gut answer of just a little over 50%. I find that physics people are pretty good at solving the problem.

I would also REALLY hope that somebody who is applying for a job in finance understands the bond prices and interest rates, but I suppose that does make it a good fizz buzz type question.