Emily, that's not the lazy option, the lazy option is to go to anydice.com and get this:
http://anydice.com/program/c40
Oh, and it does it by probability exploration, not by doing a gazillion trials ;) Oh, and it is fast!
EDIT: Ninjaed by PseudoFenton!
EDIT2: Anydice is just so nice... you can get nice tables, bar graphs, line graphs,... check "graph" and "at most" for the curves for GURPS probabilities