AMC 12 2003a Problem 10

Al, Bert, and Carl are the winners of a school drawing for a pile of Halloween candy, which they are to divide in a ratio of $3:2:1$, respectively. Due to some confusion they come at different times to claim their prizes, and each assumes he is the first to arrive. If each takes what he believes to be the correct share of candy, what fraction of the candy goes unclaimed?

$\mathrm{(A) \ } \frac{1}{18} \mathrm{(B) \ } \frac{1}{6} \mathrm{(C) \ } \frac{2}{9} \mathrm{(D) \ } \frac{5}{18} \mathrm{(E) \ } \frac{5}{12}$