A metalworker has a metal alloy that is 15 % copper and another alloy that is 55 % copper. how many kilograms of each alloy should the metalworker combine to create 120 kg of a 39 % copper alloy?

Qty · % = Total

Alloy 1: x · 15% =.15x

Alloy 2: 120-x · 55% =.55 (120 - x) → 66 -.55x

Mixture: 120 · 39% =.15x + 66 -.55x

120 ·.39 = 66 -.40x

46.8 = 66 -.40x

-19.2 = -.40x

48 = x

Alloy 1:x = 48

Alloy 2: 120 - x = 120 - 48 = 72

Answer: The metalworker should use 48 kg of the 15% copper and 72 kg of the 55% copper.