I enjoy interviews with these types of questions because I am nerdy enough to have wasted some of my youth buried up to the nose in logic puzzles and riddles, a

I enjoy interviews with these types of questions because I am nerdy enough to have wasted some of my youth buried up to the nose in logic puzzles and riddles, and sensible enough to research employers and interview tips to find out who asks these questions and which ones are commonly asked, and lucky enough to have studied mathematics and computer science at a university which teaches the birthday puzzle (probability) in its first term. Between all these, I'm not too bad at these questions, and very little of the reason for that is innate. Anecdote: I was asked at interview "If I was in a room with 27 people and made a bet with you for $5 that no two people in the room shared a birthday, would you take the bet?". Answering "Yes", the reasoning being "I've done basic probability and covered the birthday puzzle, so know off the top of my head that you only need 23 people to get even odds" probably flagged me as arrogant (I had to explain why it was 23) but I felt good saying it. Interestingly the interview said only 1 in 10 people - interviewing for a fairly technical position that required a computer science degree - had encountered this before.