| You have three containers. One has only red marbles, one has only blue marbles and the third has an equal number of red and blue marbles. The labels on the containers have intentionally been switched so that each container is now marked incorrectly.
Your job is to relabel the containers correctly. Of course you could just look in the containers to find out which labels match, but can you do it without looking into each container? Reach into any one of the containers and select one marble. Can you now correctly label all three containers? If not, select a second marble from any container. What is the fewest number of marbles you need to inspect in order to correctly label each container?