What to see

Observe the triangle above. It consists of 4 coloured pieces, and a missing square. Now press the “re-order pieces” button. Three pieces move to another place, the overall shape seems the same, but the square is no longer missing!

What to do

Repeat the re-arrangement of the pieces and have a go at the puzzle. Where is the missing square? What happens here? Be assured that this is no computer trick, it would work just as well with pieces cut from cardboard. In fact, it’s great fun to do so and make a nice puzzle for your dear one(s).


    1. Should I really tell you the solution? You probably have figured it out by now. Hint: it does belong into this optical illusion collection, and there’s a good reason it’s sitting in the “Geometric- & Angle Illusions” category.
    2. Martin Gardner popularised this in Scientific American, the original inventor seems to be Paul Curry, a New Yorkean magician.


Martin Gardner (1965) Mathematics, Magic and Mystery, New York, Dover Publ.

Good explanation at Grand Illusions

Geometrical Paradoxes

Ok, ok, here’s the solution.

Created: 2008-Feb-12

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Last update 2018-06-12 by Michael Bach