The mole

In an experiment, 1.0 g of impure copper(II) carbonate is heated strongly until it decomposes completely to copper(II) oxide and carbon dioxide. The mass of copper(II) oxide obtained is 0.64 g. What is the percentage purity of the original sample of copper(II) carbonate?

$M_r(CuCO_3)=124,\ M_r(CuO)=80$