SOLUTION: Sam has 5 rings each weighing 18g, 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 75%. How mu

Question 460436: Sam has 5 rings each weighing 18g, 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 75%. How much silver should he add?
Found 2 solutions by richwmiller, lwsshak3:
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
s=.1*(18)=1.8
g=.9*(18)=16.2
from view of silver
1.8+x/(18+x)=.25
x=3.6
add 3.6 g of silver
from view of gold
16.2/(18+x)=.75
x=3.6
add 3.6 g of silver

Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
Sam has 5 rings each weighing 18g, 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 75%. How much silver should he add?
..
let x=grams of silver to add
18*10%=1.8g = initial grams of silver in alloy
18*90%=16.2g=initial grams of gold in alloy
1.8+x=total grams of silver in new alloy
..
ratio of silver to gold in new alloy=25/75=1/3=(1.8+x)/(16.2)
3(1.8+x)=16.2
5.4+3x=16.2
3x=16.2-5.4=10.8
x=10.8/3=3.6 g
ans:
The amount of silver to add to reduce the gold content to 75%=3.6g
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