The shortest path for a spider to reach a fly isn't the obvious one
In a rectangular room 30 feet long, 12 feet wide and 12 feet high, a spider sits on one end wall, a foot below the ceiling and centred. A fly sits on the opposite wall, a foot above the floor and centred. Crawling only along the surfaces, what is the shortest possible distance from spider to fly?
Reveal the answer
40 feet — not the 42 feet you get from the 'obvious' route across the ceiling and down the far wall. The shortest path unfolds across five of the room's six faces, which only becomes visible if you flatten the room into a net and draw a straight line between the two points. Henry Dudeney posed it in the Weekly Dispatch in 1903 and later collected it in The Canterbury Puzzles (1907); it remains a classic demonstration that 3D shortest-path intuition is unreliable.
— Henry Ernest Dudeney, The Canterbury Puzzles — 1907 (puzzle first published 1903)
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