This puzzle has been driving me crazy. So there are three guys in a hotel and they order a pizza. It costs $30. Each guy chips in $10. But when the pizza delivery person gets back to the pizza place with the $30, it turns out the pizza really only costs $25. So he goes back to the guys to return their change, pockets $2 since they didn't tip him, leaving $1 for each of the men. That means each guy paid $9, plus the tip, that's only $29. Where is the other dollar? Pleeeeeeez answer this.
-- [Too distraught to sign it]
Get three of these a year. Homework assignment? That's why I waited until summer to answer. The trick is in how the question is worded. Each man paid $9, but that already includes each man's share of the tip. What you need to do is add the $3 change to the $9 x 3, and waaah laaah, you get $27 + $3 = $30, everybody's happy. Except the guys who got Fs on their homework, I guess.