Explanation

Time period of simple pendulum is $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ T = 2\pi\sqrt{\frac{l}{g}}$ Or $\frac{\mathrm{\Delta}T}{T} = \frac{1}{2}\left( \frac{\mathrm{\Delta}l}{l} - \frac{\mathrm{\Delta}g}{g} \right)$ Or $\ \ \ \ \ \ \ \ \ \ \ \frac{\mathrm{\Delta}g}{g} = \frac{\mathrm{\Delta}l}{l} - \frac{2\mathrm{\Delta}T}{T}$ $\therefore$ Maximum percentage error in equation $\frac{\mathrm{\Delta}g}{g} \times 100 = \frac{\mathrm{\Delta}l}{l} \times 100 + \frac{2\mathrm{\Delta}T}{T} \times 100$ $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 1 \times 100 + 2 \times 2 \times 100$ $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 5 \times 100 = 5\%$