Homework Help: math

Posted by sakena on Monday, February 20, 2012 at 4:11pm.

Anne and Nancy use a metal alloy that is 23.5% copper to make jewelry. How many ounces of a
21% alloy must be mixed with a 30% alloy to form 108 ounces of the desired alloy?

math - Steve, Monday, February 20, 2012 at 7:00pm
you want the final 108 oz to be 23.5% copper. That means it contains 25.38 oz of copper

So, if there are x oz of 21% alloy,

.21x + .30(108-x) = .235(108)
.21x + 32.4 - .30x = 25.38
.09x = 7.02
x = 78

so, she uses 78 oz of 21% and 30 oz of 30%

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