Back in 1971, these three people go to a hotel and to share a room. The manager tells them the room is $30, so they each give him $10. When they get to their hotel room, the manager drops by to explain that a special $25 rate is in place, and returns $5 in ones to them. They each take a dollar, and give back the remaining $2 to the manager for his honesty.

Now, if each of the three people paid $10 and got $1 back, they paid $9 a piece, or a total of $27 (3 × 9). The manager gets $2, so that adds up to $29.