SOLUTION: How much pure copper must be added to 50 kg of an alloy containing 12% copper to raise the copper content to 21%?

Question 911345: How much pure copper must be added to 50 kg of an alloy containing 12% copper to raise the copper content to 21%?
Found 2 solutions by lwsshak3, josmiceli:
Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
How much pure copper must be added to 50 kg of an alloy containing 12% copper to raise the copper content to 21%?
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let x=amt of pure copper to add:
12%*50+100%x=21%(50+x)
6+x=10.5+.21x
.79x=4.5
x=5.7
amt of pure copper to add: 5.7 kg
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
Let = kg of pure copper to be added
kg of copper in 12% alloy
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5.696 kg of pure copper must be added
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check:

OK
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