Metalworker problem

Question

A metalworker has a metal alloy that is 20% and another alloy is 60% copper. How many kilograms of each should he use to make 120kg of 52% copper?

Answer 1

(x kg)(20%) + (120 - x kg)(60%) = (120 kg)(52%)

20x + 7200 - 60x = 6240

-40x = -960

x = 24 kg of 20% copper

120 kg - 24 kg = 96 kg of 60% copper