Mixture Problem A jeweler has five rings, each weigh- ing 18 g, made of an alloy of 10% silver and 90% gold. She decides to melt down the rings and add enough silver to reduce the gold content to 75%. How much silver should she add?

Explanation:

Total weight of 5 rings

= 18 x 5

= 90 g

silver = 10% of 90 g

= 9 g

gold = 81 g

Let silver added = x gm

Total weight = 90 +x

75% of (90+x) is gold

= 3/4 x  (90+x)g is  gold

So  3/4 x  (90+x)  = 81

(90+x)  = 81 x 4 / 3

= 108

x = 18 g

silver to be added = 18g .