Math Puzzle: Find All the Squares

This square is divided into 36 smaller squares.

A 6-by-6 square checkerboard.

Amanda Montañez

If you put several of these small squares together, you can form larger squares. You can see two such squares here as an example:

Same checkerboard as above but with nine squares combined into one square and another four squares combined into a smaller square.

Amanda Montanez

How many squares are there to discover in total?

There are 91 squares in total. Because the big square has a side length of 6, there are six different square sizes: squares with lengths 1, 2, 3, 4, 5 and 6.

You can find 36 squares with length 1, 25 squares with length 2, 16 squares with length 3, nine squares with length 4, four squares with length 5 and one square with length 6. In total, there are 36 + 25 + 16 + 9 + 4 + 1 = 91 squares.

In general, the total number of squares, represented by A, in a similarly divided square with side length n can be written as:

A = n2 + (n – 1)2 + (n – 2)2 + (n – 3)2 ... + (nn)2

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This puzzle originally appeared in Spektrum der Wissenschaft and was reproduced with permission.

Hans-Karl Eder is a German mathematician, educator and author who also works as a MINT ambassador to get young people interested in mathematics, computer science, natural sciences and technology.

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