did you bring enough to share?

In the old Bill Cosby Show, Chet Kincaid was a PE teacher who, in one memorable episode, substituted for an algebra teacher. (Come to think of it, that episode was probably my first exposure to algebra!) Does anyone remember the problem that stumped him? It was of this form: A customer buys some candy at p cents/pound and some other candy at q cents/pound; the total weight is m pounds and the total price $k; how much of each kind of candy?

I was reminded of this by a rant about the importance of algebra.