SOLUTION: A certain metal is 40% copper. How many kilograms of this metal must be mixed with 60 kilograms of a metal that is 70% copper to get a metal that is 50% copper?

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Question 651004:
A certain metal is 40% copper. How many kilograms of this metal must be mixed with 60 kilograms of a metal that is 70% copper to get a metal that is 50% copper?

Found 2 solutions by josmiceli, lwsshak3:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = kg of 40% metal needed
+.4x+ = kg of copper in 40% metal
+.7%2A60+=+42+ kg of copper in 70% metal
+%28+.4x+%2B+42+%29+%2F+%28+x+%2B+60+%29+=+.5+
+.4x+%2B+42+=+.5%2A%28+x+%2B+60+%29+
+.4x+%2B+42+=+.5x+%2B+30+
+.1x+=+12+
+x+=+120+
120 kg of the 40% metal are needed
check:
+%28+.4%2A120+%2B+42+%29+%2F+%28+120+%2B+60+%29+=+.5+
+%28+48+%2B+42+%29+%2F+180+=+.5+
+90%2F180+=+.5+
+90+=+.5%2A180+
+90+=+90+
OK

Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
A certain metal is 40% copper. How many kilograms of this metal must be mixed with 60 kilograms of a metal that is 70% copper to get a metal that is 50% copper?
**
let x=kg of 40% copper to be mixed
x+60=kg of 50% mixture
..
40%x+70%*60=50%(x+60)
.4x+42=.5x+30
.1x=12
x=120
kg of 40% copper to be mixed=120