Can you plant 9 trees so they form exactly 10 straight rows of 3 trees each?
An orchard owner wants to plant 9 trees so that they line up into 10 different straight rows, each passing through exactly 3 of the trees — no more, no less. Is this geometrically possible, or does the math run out of room before the rows do?
Reveal the answer
Yes — it's achievable, using an arrangement related to the Pappus configuration from projective geometry, where several of the rows cross through the middle of the orchard at different angles. The puzzle was first posed in 1821 by John Jackson in Rational Amusement for Winter Evenings, and mathematicians still study how many more rows even bigger tree counts can squeeze out.
— John Jackson, Rational Amusement for Winter Evenings — 1821