You have three boxes. 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 boxes have intentionally been switched so that each box is now marked incorrectly.

Your job is to relabel the boxes correctly. Of course you could just look in the boxes to find out which labels match, but can you do it without looking into each box? Reach into any one of the boxes and select one marble. Can you now correctly label all three boxes? If not, select a second marble from any box. What is the fewest number of marbles you need to inspect in order to correctly label each box?

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