[Illustration]
Inside a rectangular room, measuring 30 feet in length and 12 feet in
width and height, a spider is at a point on the middle of one of the end
walls, 1 foot from the ceiling, as at A; and a fly is on the opposite
wall, 1 foot from the floor in the centre, as shown at B. What is the
shortest distance that the spider must crawl in order to reach the fly,
which remains stationary? Of course the spider never drops or uses its
web, but crawls fairly.