You have sheets of 42-cent stamps and 29-cent stamps, but you need at least $3.20 to mail a package. What is the least amount you can make with the 42- and 29-cent stamps that is sufficient to mail the package?
A contest problem such as this is probably most easily solved by tabulating the possible combinations, using 0 through ceiling(total/greater value) of the greater-value stamp and computing the necessary number of the smaller stamp and the total postage involved. The particular example above would be solved with a 9-row table, showing the minimum to be $3.23, made with 7 42-cent stamps and 1 29-cent stamp.
Is there a better algorithm for solving this kind of problem? What if you have more than two values of stamps?