Calculate the probability of seeing a landmark when starting at a given point and walking straight in a random direction
Haskell, 65 63

import Data.Complex
(s,l)%d=100*min(asin(d/magnitude(s-l))/pi)1


Use like (xstart:+ystart, xlandmark:+ylandmark) % distance.  Gives result in percent.  Why is it so expensive to load modules in Haskell?!?

Note that there is no if/then/else, pattern matching, etc. in this code, min does the magic.