Twenty-four matchsticks can be arranged to form a grid of squares as in
the picture. You may have seen a puzzle that asks if you can remove
four matchsticks without moving any of the others, so that only five
squares remain. If that's too easy, try to leave four squares, or six
squares ... or three squares, or two squares. Can you leave seven or eight
squares, or even nine squares? In each case, the rules are the same:
you must remove exactly four matches, and the other twenty must remain
in their original positions.