Question 1205470
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There is perhaps a bit of confusion with the use of the word "part" in the statement of the problem.  Change "what part of the whole" to "what fraction of the whole" for clarification.<br>
4 parts of brass and 3 parts of copper means that out of every 7 parts of the alloy 4 parts are brass and 3 parts are copper.  So the fraction of the whole that is copper is 3/7.<br>
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As a couple of other tutors have pointed out, this could be a valid math question, but if we pay attention to the science, it is not a valid question.<br>
Brass is an alloy of copper and zinc, so it is impossible to know what fraction of the alloy is copper.<br>
If we ignore the science and treat it solely as a math problem, then the fraction of copper in the alloy is 3/7; if we pay attention to the science, then we don't know.<br>