Pat Bellew has a daily blog with excellent math history: On This Day in Math. Today’s has a great gif of the Haberdasher’s Puzzle by Dudeney. Pat writes:

b. 4-10-1857 Henry Ernest Dudeney (pronounced with a long “u” and a strong accent on the first syllable, as in “scrutiny”). He was England’s greatest maker of puzzles of mathematical interest, publishing six books of puzzles. His first work appears under the pseudonym “sphinx.” Although he never met Sam Loyd, they were in frequent correspondence and informally exchanged ideas. … Some of Dudeney’s most famous innovations were his 1903 success at solving the Haberdasher’s Puzzle (Cut an equilateral triangle into four pieces that can be rearranged to make a square) and publishing the first known crossnumber puzzle, in 1926. In addition, he has been credited with inventing verbal arithmetic and discovering new applications of digital roots.

Pat points out that the Kindle edition of the Canterbury Puzzles is free!

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The elegant and magical Haberdasher puzzle.

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This gem is an astonishing discovery of Henry Dudeney, famous creator of puzzles. The puzzle asks to dissect an equilateral triangle into four pieces and to rearrange them into a perfect square.

Moreover, the four pieces can be hinged together; if you turn them over one direction, you get the square, the other direction results in the triangle. If you’re a woodcrafter, constructing a wooden version would be a challenge ;)

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