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By mass, Yellow Gold 18K is made up of 75% of Gold (Au), 15% of Silver (Ag) and the remainder is made up of Copper (Cu), by mass.
(a) Find, by mass, Au : Ag : Cu, giving your answer in the simplest form. 
(b) A goldsmith is tasked to make a piece of jewellery with Yellow Gold 18K. With 2.25g of Silver, how much of gold and copper would be needed to form the alloy? 
(c) If this piece of jewellery is to be melted into liquid alloy
(i) Find is the volume of the alloy. 
(ii) Compare the volume with that of a 15g of pure 24 carat gold, which has a greater volume – Yellow Gold 18K or 24 carat gold? 
Given that the density of Gold is 19.3 g/cm3, Silver is 10.49 g/cm3 and Copper is 8.92 g/cm3.
Watch the following clip for background info that would help you understand the context of the question better:
Mass, volume and density are related by an equation: density = mass ÷ volume