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A serving tray of brass weighs 21 oz. The brass is an alloy of 70 percent copper & 30 percent tin. What is the weight of the copper in the tray?

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kborgeson eNotes educator | Certified Educator

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When you have an object that is a certain percent of one metal combined with a second metal we can see then how the two metals work together to make a whole brass tray. 

If the whole tray is 100%, and the problem tells you that out of this 100%, 70% is copper and 30% is tin.  With this information you can use your percents to find out how much of each metal is present in the entire tray.

Since the whole tray weighs 21 oz., you should ask yourself what is 70% of 21 oz.  ...

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cburr eNotes educator | Certified Educator

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