I’ve been asking a lot of people this question to get a sense for how intuitive it is. So far, the only person to get it right on the first try was my dad the economist, and the responders included some financial professionals.
The question is: If you are faced with a pot-sized bet on the river and are choosing between calling and folding, how often must you have the best hand to make a call profitable? For example, say there is $1 in the pot. Your opponent bets $1. You can either fold, in which case you don’t put in any more money and your opponent takes the pot; or you can match the $1 bet. Then you both show your hand and whoever has the best hand wins the $3 pot. How often do you need to have the best hand to make calling a good play?