Math CentralQuandaries & Queries


Question from Lisa, a parent:

What is the karat count of gold in a bracelet that contains 15g of gold and 5 g of silver?

Hi Lisa,

According to Wikipedia one karat is 1/24 purity by weight.



X is the carat rating of the material,
Mg is the mass of pure gold or platinum in the material, and
Mm is the total mass of the material.

(In the United States and canada the spelling is karat.)

Your bracelet has 15 g of gold in a total mass of 20 g so the number of karats is

24 × 15/20 = 18.


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