How much of an alloy that is 40 % copper should be mixed with 300 ounces of an alloy that is 80 %copper in order to get an alloy that is 70 % ?copper?

Question

How much of an alloy that is 40 % copper should be mixed with 300 ounces of an alloy that is 80 %copper in order to get an alloy that is 70 % ?copper?

Answer 1

x = amount of 40% copper

 

300 = amount of 80% copper

 

x + 300 = total amount of copper = amount of 70% copper

 

Set a properly weighted combination of x and 300 equal to a weighted (x+300), where the weights are the percentages in decimal form, i.e. 40% is 0.4, 80% is 0.8, and 70% is 0.7:

 

0.4x + 0.8(300) = 0.7(x + 300)

 

Solve for x:

 

0.3x = 30

 

x = 30/0.3 = 100 ounces of 40% copper