Phew, I was busting at the seams to just shut up for once about a math problem... But this reminds me of a riddle - lemme go from memory:
Suppose you're house-sitting for some up-tight rich people. You just go there to feed the fish, and that's it. They even turned the main circuit breaker off (fuse panel if you like), and locked the box. One day, you walk in to perform your duties, and absentmindedly pull the chain down on the ceiling fan. Oops, when the owners come back, the house power comes on, and so does the fan! But... based on your knowledge of fans, the pull-switch can change the speed of the motor a few times before turning it off. Taking it for certain that either three total pulls of the chain or four total pulls of the chain will leave it in the off-position, what do you do? Pull it 3 total times or 4 total times?
And as a bonus - how does that apply to this problem?