An 18-karat gold necklace is 75% gold by mass, 16% silver, and 9.0% copper. what is the mass, in grams, of the necklace if it contains 0.28oz of silver?

The  mass of necklace is 1.75 gm.

Explanation:

Given that

The total mass of necklace will be the some of the mass of silver,mass of the  gold and mass of the copper.

Mass of gold = 18 %

Mass silver = 16%

Mass copper = 9%

Lets take the mass of necklace is m

Then mass of silver will 0.16 m.

And given that mass of silver is 0.28 gm.

So

0.28 gm = 0.16 x m

m= 1.75 gm

So the  mass of necklace is 1.75 gm.