An alloy contains copper and zinc in the ratio 7 : 3. If it contains 12.6 g of copper, how much does this alloy weigh?

Given:

Ratio (Copper : Zinc) = 7 : 3

Copper = 12.6 g

Since 7 parts represent copper, 7 parts = 12.6 g

1 part = 12.6 ÷ 7 = 1.8 g

Zinc = 3 x 1.8 g = 5.4 g

Total weight = Copper + Zinc

Substituting the values in above:

Total weight = 12.6 g + 5.4 g = 18 g

The weight of the alloy is 18 g.