SOLUTION: A parts manufacturer has 40 kg of a copper and zinc alloy which contains 8 kg of zinc. Find the amount of copper which must be added if the manufacturer requires a new alloy contai

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Question 974628: A parts manufacturer has 40 kg of a copper and zinc alloy which contains 8 kg of zinc. Find the amount of copper which must be added if the manufacturer requires a new alloy containing 10% zinc.
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
Copper will dilute the Zinc.

%2840%288%2F40%29%29%2F%2840%2Bz%29=0.10

%2840%281%2F5%29%29%2F%28z%2B40%29=1%2F10

8%2F%28z%2B40%29=1%2F10

z%2B40=80

z=40


NOTE: This seemed a little easier converting fully into regular fractions than percents or mixing percents with regular fractions. Usually the choice is yours when you solve, depending on instructions.