Given
The mass of a certain 10k gold necklace is 18 grams.
Find out how many grams of gold are in the necklace.
To proof
let us assume that the gold in the necklace be x.
As given in the question
10k gold necklace i.e gold necklace is made up of the various elements with the gold.
10k gold necklace is 18 grams.
As pure gold is of the 24k.
than the equation becomes
solving
x =7.5 gram
7.5 grams of gold are in the necklace .
Hence proved