In a simple pendulum experiment for determination of acceleration due to gravity $\left(\mathrm{g}\right)$, time taken for $20$ oscillations is measures by using a watch of $1$ second least count. The mean value of time taken comes out to be $30\mathrm{ }\mathrm{s}$. The length of the pendulum is measured by using a meter scale of least count $1 \mathrm{m}\mathrm{m}$ and the value obtained is $55.0 \mathrm{c}\mathrm{m}$. The percentage error in the determination of $\mathrm{g}$ is close to