Question 993621: A jeweler has 5 rings, each weighing 18 grams, made of an alloy of 18% silver and 90% gold. She decides to melt down the rings and added enough silver to reduce the gold content to 75%. How much silver should she add?
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! A jeweler has 5 rings, each weighing 18 grams, made of an alloy of 18% silver and 90% gold. She decides to melt down the rings and added enough silver to reduce the gold content to 75%. How much silver should she add?
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Weight of rings:: 90 grams
If the result is 75% gold, it must be 25% silver.
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Equation:
silver + silver = silver
18%(weight) silver + 100%(weight) silver = 25%(weight) silver
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0.18*90 + 1*x = 0.25(90+x)
Multiply thru by 100 to get::
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18*90 + 100x = 25*90 + 25x
Solve for "x", which is the amt. of 100% silver you add
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100x-25x = 25*90-18*90
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75x = 7*90
x = (19/15)*7
x = 8.8667 grams (amt. of 100% silver to add)
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Cheers,
Stan H.
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