GMAT Quantitative Reasoning Practice Test 1

To make this problem easier, assume the initial cost of the jacket was $\mathrm{\$}100$. The first markdown of $20\%$ would save you $\mathrm{\$}20$, bringing the cost of the jacket to $\mathrm{\$}80$. For the second markdown, you should be finding $20\%$ of $\mathrm{\$}80$, the new cost of the jacket. $20\%$ of $80=0.20\times 80=16$. If you save $\mathrm{\$}16$ the second time, the final cost of the jacket is $80-16=\mathrm{\$}64$. Since the initial cost was $\mathrm{\$}100,\mathrm{\$}64$ is $64\%$ of this price.