Shafted From Henry Dudeney: A ball 13 inches in diameter has a 5-inch hole drilled through the center. How deep is the hole? SelectClick for Answer> Pythagoras solves this neatly: x2 + 25 = 169; x = 12. Curious addendum: If you now hold the hole’s depth constant at 12 and vary its width, adjusting the object’s diameter accordingly, the object’s volume remains constant. (Thanks, Thomas.) January 23, 2010January 23, 2013 | Puzzles