Problem Sets

Hey...would any of you fellow professors like to contribute a problem or two???  I am tired of mine!  Just keep them simple and to the point.  Something that illuminates a concept, and that could  be worked out by hand (or using the calculators in this web site) in 5-minutes or so.  Numerical problems only,  no true-or-false or short-answer problems please.

Also, please email your solution(s) to me.