SOLUTION: Please help me solve this. I've been trying this for hours now. "A jewel has five rings, each weighing 18grams, made of an alloy of 10% silver and 90% gold. He decides to melt do

Algebra ->  Customizable Word Problem Solvers  -> Mixtures -> SOLUTION: Please help me solve this. I've been trying this for hours now. "A jewel has five rings, each weighing 18grams, made of an alloy of 10% silver and 90% gold. He decides to melt do      Log On

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Question 982426: Please help me solve this. I've been trying this for hours now.
"A jewel has five rings, each weighing 18grams, made of an alloy of 10% silver and 90% gold. He decides to melt down the rings and add enough silver to reduce the gold content to 7.5%. How much silver could he add? "
Found 2 solutions by josgarithmetic, KMST:
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
5*18 grams of the alloy;

x, how many grams of silver to add
%285%2A18%2A90%29%2F%285%2A18%2Bx%29=7.5

Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
The total amount of metal in that jewel amounts to
5%2A%2818g%29=90g .
%2290%25%22=90%2F100=0.9 , so the 0.9 of the rings in the jewel is gold.
The total amount of gold in that jewel amounts to
5%2A%2818g%29%2A0.9=81g .
If that 81g is going to be %227.5%25%22=7.5%2F100=0.075 of a new total amount x , then
0.075x=81g--->x=81g%2F0.075--->x=1080g .
Obviously the total amount of metal added was
1080g-90g=990g , and all that was added silver,
so the amount of silver he could add is highlight%28990g%29 .