This is a question from a precalculus class that I'm a TA for.
You build a box that has a volume of 100 cubic feet. It takes two people ten minutes to spray paint this box. How many minutes does it take three people to spray paint a similar box that has a volume of 500 cubic feet? Assume that the area of surface to be covered is proportionate to both the number of people working and the time spent spray painting.
A student just asked me how to answer it, so I figured I'd write up the correct calculations and post it online to help anyone else who may wander across it.