Saw this one on Professor Layton 2.
To analogue clocks hang side by side on a wall. One of the clocks is slightly fast, the other slightly slow. One day at noon, you set both clocks correctly. After one hour you notice that the fast clock displays 1:01 and the slow clock reports the time as 12:59. Assuming the clocks continue to be fast and slow at the same rate, how long before both clocks agree on the time again?
Professor Layton and the Diabolical Box - sequel to the Curious Village. Another great Nintendo DS puzzle game.