I heard this on a podcast, I won't say which one in order to discourage people from looking up the answer.
Place three digits, 2, 7 and one other, in an expression that equals 8. You can use +, -, *, / and exponentiation. Decimal points and parentheses may be used freely, but each digit may only appear once in the expression. Do this nine times where the remaining digit is 1 through 9. When you're done you'll have 9 expressions, each consisting of only three digits (2, 7 and the remaining digit of 1 through 9) and all equal to 8.
For example, when the third digit is 1, the expression is:
7 + 2 - 1 = 8
Now find the remaining 8 expressions.
--Percy