Answer
18 grams
Work Step by Step
Total amount of alloy is 5 times 18 gram ring = 90 grams
Content of silver in the alloy is 10% and we want 25% content (75% gold content) and we will be adding 100% pure silver 1 times x (1 represents 100% and x is the amount of pure silver in grams)
0.1(90)+1x=0.25(90+x)
9+x=22.5+0.25x
0.75x=13.5
x=18
