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 metal worker combine to create 90 kilograms of a 51% copper alloy?

Answer 1

x + y = 90
y = 90 - x

0.15 x + 0.75 y = 0.51 (90)

0.15 x + 0.75 (90-x) = 0.51 (90)
0.15x + 67.5 -0.75x = 45.9
21.6 = 0.6 x
x = 36 kg -- 15% Cu

y = 90 - x
y = 90 - 36
y = 54 kg -- 75% Cu