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?
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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