H. E. Dudeney, Amusements in Mathematics (1917) No. 209 · Puzzles · Geometrical puzzles
The Twenty-One Trees
A gentleman wished to plant twenty-one trees in his park so that they should form twelve straight rows with five trees in every row. Could you have supplied him with a pretty symmetrical arrangement that would satisfy these conditions?
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H. E. Dudeney, Amusements in Mathematics (1917) · No. 209
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