Question

A jeweler has five rings, each weighing 18 grams, 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 45 %. How much silver should he add?

Answer 1

He should add 55% of silver.
10% = 1.8
5% = 0.9
1.8 * 5 = 9
9 + 0.9 = 9.9

He should add 9.9g of silver.