The Three Envelopes Problem

Puzzle: You have three envelopes: one contains a check for $100, another $200, and another $300. You pick one at random and see that it has $200. You can keep it or switch. Should you switch?

Answer: Switching doesn’t change your odds as each envelope was equally likely at the start. This puzzle illustrates how perceived probability doesn’t change once the choice is made, similar to Monty Hall without the host’s influence.