Fun with numbers.

Ask a friend to write down any number, multiply it by 3, add 6, divide by 3, and subtract the number first used. Then tell him the answer. It will always be 2, no matter what number he chose to begin with.

Have a classmate write down any number, then double it, add 9, subtract 3, divide by 2, and subtract the number she started with. Then tell her the answer. It will always be 3.

Think of any three-digit number. Add 7, multiply by 2, subtract 4, divide by 2, and subtract the number you started with. The answer will always be 5.