Chapter 10, Problem 75E

A laboratory test of $12.8\text{g}$ of aluminum ore yields $1.68\text{g}$ of aluminum. If the aluminum compound in the ore is ${\text{Al}}_{\text{2}}{\text{O}}_{\text{3}}$ and it is converted to the pure metal by the reaction $2{\text{Al}}_{\text{2}}{\text{O}}_{\text{3}}\left(\text{s}\right)+3\text{C}\left(\text{s}\right)\to 4\text{Al}\left(\text{s}\right)+3{\text{CO}}_{\text{2}}\left(\text{g}\right)$, what is the percentage of ${\text{Al}}_{\text{2}}{\text{O}}_{\text{3}}$ in the ore?