DAY 269
You have three boxes labelled PEACHES, ORANGES, and PEACHES AND ORANGES. All three boxes are labelled incorrectly. How can you label the boxes correctly by opening just one box and removing just one piece of fruit?

Answer:

Open the box labelled PEACHES AND ORANGES. Since it is labelled incorrectly, it should contain either all oranges or all peaches. If you pull out an orange, you know that box should be labelled ORANGES. Now switch the labels on the other two boxes and they will all be correct.