Joe has a ring weighing 16 grams made of an alloy of 20% silver and the rest gold. He decides to melt down the rings and add enough silver to reduce the gold content to 69% . How many grams of silver should he add?

Answer 1

considering just the mass of the silver,

(.20)(16)+x = (.31)(16+x)
x =2.55

so, add 2.55g of silver