Percentage yield and purity

A sample of hydrated copper(II) sulfate, $\text{CuSO}_4\cdot 5\text{H}_2\text{O}$, is heated until all the water is removed. If 2.50 g of the hydrated salt gives 1.60 g of anhydrous $\text{CuSO}_4$, what is the percentage by mass of water in the hydrated salt?