SOLUTION: A jeweler has 3 rings, each weighing 18 g, made of an alloy of 7% silver and 93% gold. She decides to melt down the rings and add enough silver to reduce the gold content to 81%. H

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Question 839179: A jeweler has 3 rings, each weighing 18 g, made of an alloy of 7% silver and 93% gold. She decides to melt down the rings and add enough silver to reduce the gold content to 81%. How much silver should she add?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The 3 rings weigh +3%2A18+=+54+ g
The weight of the silver is +.07%2A54+=+3.78+ g
The weight of the gold is +.93%2A54+=+50.22+ g
Let +x+ = grams of silver to be added
to reduce the gold content to 81%.
----------------------------------------
If the gold content is to be 81%, the silver content
will be +100+-+81+=+19+%
+%28+x+%2B+3.78+%29+%2F+%28+x+%2B+54+%29+=+.19+
+x+%2B+3.78+=+.19%2A%28+x+%2B+54+%29+
+x+%2B+3.78+=+.19x+%2B+10.26+
+.81x+=+10.26+-+3.78+
+.81x+=+6.48+
+x+=+8+
-----------------
8 g of silver must be added
check:
+%28+x+%2B+3.78+%29+%2F+%28+x+%2B+54+%29+=+.19+
+%28+8+%2B+3.78+%29+%2F+%28+8+%2B+54+%29+=+.19+
+11.78+%2F+62+=+.19+
+11.78+=+.19%2A62+
+11.78+=+11.78+
OK