Oil is extracted from mustard seeds having $20 \: \mathrm{wt} \%$ oil and $80 \: \mathrm{wt} \%$ solids, using hexane as a solvent. After extraction, the hexane-free residual cake contains $1 \: \mathrm{wt} \%$ oil. Assuming negligible dissolution of cake in hexane, the percentage oil recovery in hexane is $\_\_\_\_\_ \%$ (rounded off to the nearest integer).
