Richard Wiseman posted a cool one recently, on his blog.
Imagine you have to make the number 8 from the numbers 4, 7, 6, and 3. You can add, subtract, multiply, or divide to make the number 8. (No exponents, logs, or other operations.)
4 + 7 - 6 + 3 = 8
So, can you make the number 24 with 5...