Jeff's school was recycling paper the school had one box for white paper only and one box for colored paper only and on box for colored and white paper both. Someone messed around with the boxes one day and mixed up all the labels. Here is the situation. One box has only white paper in it. One box has only colored paper in it. One box has colored and white paper in it. All the labels are wrong. How can Jeff be certain of labeling the boxes correctly by only being able to grab one piece of paper from one of the boxes. All the pieces of paper feel the same.

If the paper he should pick a paper from the white and coloured box.

Since the label is wrong, the colour that he gets will be the colour label of the box.

He places the correct label there from the two other boxes.

The label he didn't touch yet is a wrong label and you switch it with the only label you haven't put in place yet.

You're done! :)

Here's some more pictured case, which you'll understand perhaps better.

Picks one from W+C (white and coloured) -> white.
Removes label from box labeled W and places it on current W+C box.

Puts label W+C on the box currently labeled C.

Takes label C to box with now no label.

If it were red, then:

Picks one from W+C (white and coloured) -> coloured.
Removes label from box labeled C and places it on current W+C box.

Puts label W+C on the box currently labeled W.

Takes label W to box with now no label.