Weegy: 3.3
let
x = lbs of 15% alloy
30 - x = lbs of 9% alloy
so
0.15x + 0.09(30 - x) = 0.11(30)=3.3 User: An alloy of copper is 10% copper and weighs 25 pounds. A second alloy is 18% copper. How much (to the nearest tenth lb.) of the second alloy must be added to the first alloy to get a 13% mixture. Weegy: ok, so the total weight of the first alloy is 25 pounds and since it is 10% copper, that means that 2.5 pounds is copper.
We want to have 13% copper. [ remember that percentage is the following:
(part/whole)*100
so to match our problem:
(total copper/total weight)*100
Well right now we have 2.5 pounds of cppper and a total weight of 25. We are going to add some of the 2nd alloy, but we dont' know how much, so let's say x.
that means we have a total of 25 + x pounds of total weight and :
2.5 + .18(x) total copper.
So we have:
(2.5+.18x)/(25+x) = 13/100 because it's supposed to equal 13%
cross multiply:
250 + 18x = 325 + 13x
5x = 75
x = 15
therefore we must add 15 pounds of alloy 2 ] (More)

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