Jumping in Puddles

Answer: Tuesday Teaser #4

Problems like this are always worth illustrating with diagrams. We’ll label the two chambers that contain bullets in red and the empty chambers in grey. Because Bob didn’t blow his brains out, he must have fired from one of the four grey chambers. Now for three of these chambers, the next chamber to be fired will be empty, so we have a 3/4 chance of surviving if we keep the arrangement as it is. On the other hand, if we decide to spin the barrel, each position is equally likely and so the chance of surviving is 2/3.