SOLUTION: How much of an alloy this is 20% should be mixed with 500 ounces of alloy that is 80% copper in order to get and alloy that is 30% copper?

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Question 632119: How much of an alloy this is 20% should be mixed with 500 ounces of alloy that is 80% copper in order to get and alloy that is 30% copper?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = ounces of 20% alloy needed
+.2x+ = ounces of copper in +x+ ounces
+.8%2A500+=+400+ ounces of copper in 80% alloy
---------------
+%28+.2x+%2B+400+%29+%2F+%28+x+%2B+500+%29+=+.3+
+.2x+%2B+400+=+.3%2A%28+x+%2B+500+%29+
+.2x+%2B+400+=+.3x+%2B+150+
+.1x+=+400+-+150+
+.1x+=+250+
+x+=+2500+
2500 ounces of 20% alloy are needed
check:
+%28+.2%2A2500+%2B+400+%29+%2F+%28+2500+%2B+500+%29+=+.3+
+%28+500+%2B+400+%29+%2F+3000+=+.3+
+900+=+.3%2A3000+
+900+=+900+
OK