$\frac{\mathrm{d} \mathrm{R}_{\mathrm{eq}}}{\mathrm{R}_{\mathrm{eq}}^{2}}=\frac{\mathrm{dR}_{1}}{\mathrm{R}_{1}^{2}}+\frac{\mathrm{d} \mathrm{R}_{2}}{\mathrm{R}_{2}^{2}}$

$\Rightarrow \frac{\mathrm{d} R_{e q}}{R_{e q}}=R_{e q}\left\{\frac{d R_{1}}{R_{1}} \times \frac{1}{R_{1}}+\frac{d R_{2}}{R_{2}} \times \frac{1}{R_{2}}\right\}$

$\%$ error $=2\left\{\frac{1}{3}+\frac{2}{6}\right\}$

$=\frac{4}{3} \%=1.33 \%$