How many kilograms of each alloy should the metalworker combine to create 100 kg of a 55​% copper​ alloy?

Question

A metalworker has a metal alloy that is 15% copper and another alloy that is 65% copper.

Answer 1

Let x = kg of the 15% copper

(x)(15%) + (100 kg - x kg)(65%) = (100 kg)(55%)

15x + 6500 - 65x = 5500

-50x = -1000

x = 20 kg

So, you need 20 kg of the 15% copper alloy and 80 kg of the 65% copper alloy to make 100 kg of a 55% copper alloy