So, $g=\frac{4 \pi^{2} L}{T^{2}}$
Thus, $\frac{\Delta g}{g}=\frac{\Delta L}{L}+2 \frac{\Delta T}{T}$
% error in $g=\frac{\Delta g}{g} \times 100$
$=\left(\frac{\Delta L}{L}+2 \frac{\Delta T}{T}\right) \times 100$
$=\left(\frac{(1 / 10)}{20}+2 \times \frac{1}{90}\right) \times 100=2.72 \%$
$(i)$ $\mathrm{A}_{1}=24.36, \mathrm{B}_{1}=0.0724, \mathrm{C}_{1}=256.2$
$(ii)$ $\mathrm{A}_{2}=24.44, \mathrm{B}_{2}=16.082, \mathrm{C}_{2}=240.2$
$(iii)$ $\mathrm{A}_{3}=25.2, \mathrm{B}_{3}=19.2812, \mathrm{C}_{3}=236.183$
$(iv)$ $\mathrm{A}_{4}=25, \mathrm{B}_{4}=236.191, \mathrm{C}_{4}=19.5$