And another old one:
Three people went to a restaurant, and the bill came to $25.
Each person gave the waiter a $10 note and they told the waiter to keep $2 out of the change as a tip.
The waiter took the $30 to the till, returned with $3 in coins, and gave $1 to each diner.
So each person spent $9. The meal had therefore cost $27 plus $2 for the waiter's tip. Where had the other $1 gone???
