Nathan, this problem is not as straightforward as it first appears. The hardest part for me was understanding the original question.

I worked in a lab where we had to calculate the amount of surfactant in a resinous emulsion, and it was the same type of problem. You know what the total weight should be, and you know what percentage of surfactant to one of the parts should be. It's just not a straightforward percent problem. As a matter of fact, I noticed two groups of people and how they calculated this, the Mudguard type (which includes me) and the Jon Freeman type (the engineers). Mudguard sets up an equation and solves for the unknown. Jon multiplies and divides, a sequential type thinking as opposed to the other wholistic type thinking. I observed that the people trained as engineers did this kind of calculation so much that their thought patterns were established to do it the fastest way. Also, one engineering-school-trained guy used an ancient Hewlett-Packard calculator that required him to enter the numbers, then enter the function to perform.

We joked that the best way to hide an invention was to put it in a patent for everyone to read. The descriptions of amounts of materials used are so convoluted and hard to interpret, it's hard to duplicate the process.