how much alloy

Question

How much of an alloy that is 20% copper should be mixed with 200 ounces of an alloy that is 50% copper to get an alloy that is 30%copper?

Answer 1

 

First alloy: Assume 20% alloy has mass : A ounces; Mass of Cu in there will be : 0.2 x A ounces of Cu

Second alloy: 200 ounces 50 % alloy has 100 ounces of  Cu

Third alloy : If you mix A ounces 20% alloy to 200 ounces, mass of final mixture will be: (A +200) ounces

Final mixture has 30% of Cu : 0.3 x (A +200) ounces of Cu

 

0.2 x A + 100 = 0.3 x (A +200)

 

0.1 A = 40

A = 400 ounces

 

You need to mix 400 ounces 20% Cu  alloy to 200 ounces 50 % alloy to get  600 ounces 30 % alloy.