Where Is the 5?*
by Serhiy Grabarchuk
The four pieces shown in the illustration make up a square with the red
magic square 3x3 on it. The magic constant is 15 (each row, column and
both main diagonals add up to 15).
Click the Shuffle button to scramble the pieces. After that the Flip Over
button appears. Click it, and all the pieces will be flipped over.
Now put the pieces into a square again, this time with the blue magic
square on it. To make the task easier just follow the blue outline of the
Have you noticed something odd in the new square? Can you say where did
the little square with the number 5 disappear, and thus why did the hole
appear in the new square?
*This puzzle trick is based
on the classic Four-piece Squares paradox described in Martin Gardner's
Mathematics, Magic and Mystery book.