Author: Henry Dudeney

Henry Ernest Dudeney (1857 – 1930) was an English author and mathematician who specialized in logic puzzles and mathematical games. He is known as one of the country's foremost creators of mathematical puzzles.
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First, print and cut the pieces below. Then, arrange them so that they form a triangle and then rearrange them so that they form a square.

The solution is shown below.

What is fascinating about these dissections is that one can transform into the other by keeping the pieces attached to each other in a chain and simply rotating them around the hinge points.

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Replace every letter with a different digit between 0 and 9, such that you get a correct calculation.

The answer is 9567 + 1085 = 10652.

You can first see that M = 1. Then S = 8 or 9 and O = 0. MORE is at most 1098, and if S = 8, then E = 9, N is either 9 or 0, but this is impossible. Therefore S = 9, N = E + 1. You can check easily the 6 possibilities for (N, E) and then find the answer.