An alloy of copper is 10% copper and weighs 25 pounds. A second alloy is 18% copper. How much (to the nearest tenth lb.) of the second alloy must be added to the first alloy to get a 13% mixture.

Answer 1

add up the amount of copper in each part. It must total the amount of copper in the final alloy

.10*25 + .18x = .13(25+x)

now just solve for x