Word Problem with Percentages

Question

A copper alloy that is 40% copper is to be combined with a copper alloy that is 80% copper to produce 120 kilograms of an alloy that is 70% copper. How many kilograms of each alloy must be used?

Answer 1

Let x = amt of the 40% alloy and 120-x =amt of the 80% alloy

 

.40(x) + .80(120-x) = .70(120)

 

-.40(x) + 96 = 84

 

-.4x = -12

 

x = 30kg of 40% alloy, 90kg of 80% alloy