You are given 21 3x1 rectangular pieces to cover an 8x8 chessboard. Since the board has 64 squares, which square on the chessboard must you cut out so that the 21 given pieces exactly cover the remaining 63 squares? Or it is impossible, no matter which square you remove?
The square to remove is any one knight's move towards the center of the board, from that knight's home position.
There might be others, but I ran out of 1X3 tiles.
spoiler
