How much should the effective length of a simple pendulum be increased to increase the time period by $50 \%$ ?

$\mathrm{T} \propto \sqrt{1} \therefore \frac{\mathrm{T}_{1}}{\mathrm{~T}_{2}}=\sqrt{\frac{\mathrm{l}_{1}}{\mathrm{l}_{2}}} \therefore \frac{\mathrm{l}_{2}}{\mathrm{l}_{1}}=\frac{\mathrm{T}_{2}^{2}}{\mathrm{~T}_{1}^{2}}=(1.5)^{2}=2.25$