A mixture of $\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}$ and $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}$ is
heated until all the water is lost. If $5.020 \mathrm{~g}$ of the mixture gives $2.988 \mathrm{~g}$ of the anhydrous salts, what is the percent by mass of $\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}$ in the mixture?