<< 3 guys each gave you $10 to buy some beer, so you go to the store to pick up some beer, which only cost you $25. So you have $5 left over. You gave yourself $2 for being a cool guy. You go back and give each of the guy $1 back, so in essence they each only ditched out $9 instead of $10, for a total of $27. Now where did that extra dollar go?? >>
What extra dollar? they each pay $9, which gives $27. beer was $25, and you took the $2 that was left. I must be missing something.