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 50%?

X=40% amount

300-x=other amount

0.4x+300 (0.8) = (x+300) 0.5

expand

0.4x+240=0.5x+150

minus 0.4x both sides

240=0.1x+150

minus 150 both sides

90=0.1x

times 10 both sides

900=x

add 900oz of the 40% alloy