how many 0z of a metal containing 90% copper must be combined with 3 0z of purecopper to form an alloy containing 92% copper?

Answer 1

It's almost the same as the silt/soil problem.

Let x be the volume of metal in oz needed, then

(0.9x+3)/(x+3)=0.92
Solve for x.
Do not forget to distribute when you cross multiply.