We hope that you find this problem a good exercise for your algebra students at this time of the year. We'd appreciate any feedback you have about it - just send me email or post a reply to this message. Thanks!
--- Annie Fetter is the PoW doyen at the Math Forum. She's currently busy working on a self-guided course to train volunteer mentors so that we can respond to more and more students who submit answer to our Problems of the Week. ---