Question

A metalworker has a metal alloy that is 15​% copper and another alloy that is 75​% copper. How many kilograms of each alloy should the metalworker combine to create 100 kg of a 63​% copper​ alloy?

Answer 1

For 100kg 

15% : (100-x)0.15
75% : 0.75x

equation

(100-x)0.15 + 0.75x = 100*0.63
solve for x:

x = 80kg of 75%
20kg of 15%