An alloy is a mixture of metals. Suppose that a certain alloy is made by mixing 120 grams of an alloy that contains 42%copper with 200 grams of pure copper. Dont round

To answer the problem above, we make use of balancing of the materials before and after mixing. Let total amount of material after mixing is 320. Let x be the percent copper of the mixture and applying copper balance,

(0.42) (120 g) + (1) (200) = 320x, x = 0.7825

Thus, the mixture is 78.25% copper.