160 kg of an alloy of copper and aluminium contains 55 percent of aluminium. How much aluminium must be melted into it to make the alloy contain 70 percent of alluminium

Answer 1

let the amount of aluminum added be x kg

.55(160) + x = .7(160+x)
88 + .55x + x = 112 + .7x
.85x = 24
x = appr 28.24 kg