Brass is made from a mixture of copper and other elements. A mixture that is 80% copper is combined with a mixture that is 60% copper, resulting in 100 pounds of brass that is 65% copper. Which equation can be used to find x , the amount of 60 percent mixture used to create the 65 percent mixture?
Answer
A
0 point 6 times open paren 100 minus x close paren plus 0 point 8 x is equal to 100 times 0 point 6 5
B
0 point 6 times x plus 0 point 8 times open paren 100 plus x close paren is equal to 0 point 6 5
C
0 point 8 repeating 100 plus 0 point 6 x is equal to 0 point 6 5 times open paren 100 minus x close paren
D
0 point 8 times open paren 100 minus x close paren plus 0 point 6 x is equal to 100 times 0 point 6 5
Explanation
If x pounds are the 60% mixture, then 100 − x pounds are the 80% mixture. The copper contributed is 0.6x + 0.8(100 − x), and the finished 100 pounds contains 0.65 × 100 pounds of copper. Therefore, the equation is 0.8(100 − x) + 0.6x = 100 × 0.65, choice D.
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