Since once in a (short) while there's a question about what the interviews are like at an actual investment shop (ie, IB, hedge fund, asset manager, not "prop"), I figured I'd share one in the spirit of the holiday. This is an actual interview brain teaser used by one of the top 5 trading shop in the world in an interview for a strategist (5y+ experience, 300k+/yr): You are playing this coin game: a fair coin will be flipped five times in a row. You will win on the 3rd head. You will lose on the 2nd head. (ie, if 1 is head and 0 is tail, if the flip comes out 111, you win. if it comes out 1011, you win. if it comes ou t 1000 you lose). You start out with $100. You can bet any amount, but no more than what you have on hand at the time, before each flip. If head, you double what you bet. If tail, you lose what you bet. You want to double your initial $100 stake if you win the game (3 heads). Question: what is the size of the first bet that you should make? Hint: there is ONE right answer. It will require you coming up with the full betting strategy.