SOLUTION: Copper that was 63% pure was melted together with copper that was 90% pure to make 18 kilograms of an alloy that was 75% pure. How many kilograms of each kind were used?

Question 662906: Copper that was 63% pure was melted together with copper that was 90% pure to make 18 kilograms of an alloy that was 75% pure. How many kilograms of each kind were used?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Copper that was 63% pure was melted together with copper that was 90% pure to make 18 kilograms of an alloy that was 75% pure. How many kilograms of each kind were used?
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Equation:
copper + copper = copper
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0.63x + 0.90(18-x) = 0.75*18
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63x + 90*18 - 90x = 75*18
-27x = -15*18
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x = 10 kg (amt of 63% alloy needed)
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18-x = 8 kg (amt of 90% alloy needed)
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Cheers,
Stan H.
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