Puzzle: The fly and the Spider
A fly and a spider are inside a room measuring 30 x 12 x 12 feet. The fly is located 1 foot above the floor on one of the 12 x 12 ft walls, and 6 feet in from the side wall. The spider is on the opposite, 12 x 12 ft wall, 1 foot below the ceiling and 6 feet from the side wall. (see diagram below). The fly is trapped and cannot move, the spider is free to walk anywhere along the walls, ceiling and floor but it cannot jump or spin a web thread to climb! What is the shortest distance the spider would need to travel to get to the fly? Note the answer is not 42 feet.
The answer, 40 feet, can be obtained by "flattening" the walls as illustrated below and using Pythogoras. Note that his distance is shorter than the 42 feet the spider would have to travel if first crawling along the wall to the floor, then across the floor, then up one foot to get to the fly. The puzzle was originally posed in an English newspaper by Henry Dudeney in 1903.
The actual parth taken by the spider from a 3D perspective is as follows:
