A jeweler has 5 rings, each weighing 16 g, made of an alloy of 5% silver and 95% gold. She decides to melt down the rings and add enough silver to reduce the gold content to 80%. How much silver should she add

12 g of silver

Explanation:

5 rings and each weighs 16 g. Hence, the total mass of the 5 rings is: 5 x 16 = 80 g

Each ring contains 5% silver and 95% gold. hence:

Silver content of the 5 rings = 5/100 x 80 = 4 g

Gold content of the 5 rings = 80 - 4 = 76 g

In order to reduce the gold content of the 80 g melted ring to 80%, the silver must be increased to 20%;

5% silver is equivalent to 4 g

20% silver = 4 x 20/5 = 16 g

Since 4 g of silver is originally present in the melted mixture and 16 g of silver is required, then 12 g of silver needs to be added.