A friend of mine shared a puzzle with me this evening.
Using the numbers 1, 1, 5 and 8 exactly once, and the basic operations (+, -, /, *) and (optionally) parentheses, form an expression which has the value 10.
No trickery involved (use base 10, and concatenation of numbers is not allowed).
It should be quite simple for the math wizards here; I was able to solve it quickly because I had a hunch the solution would be the same as for a similar problem, which I already knew the solution to. This is either a hint or a bonus problem:
Make 24 out of 1, 3, 4 and 6 (same rules apply as above).