"I want you write a computer program that plays tic-tac-toe legally and runs through ALL the possible combinations of the game, and finds out the total."
The students settle down to work..
An hour later, a student gets up and proclaims "I've got it! The number of possible combinations in a game is 344,242."
At which point another student quickly replies, "I haven't finished yet, but I'm sure Fred made a mistake in his program."
(Tic Tac Toe = Noughts and Crosses)