A student measures time for 20 oscillations of a simple pendulum as $30 \mathrm{~s}, 32 \mathrm{~s}, 35 \mathrm{~s}$ and 35 s . If the minimum division in the measuring clock is 1 s , then correct mean time (in second) is

The initial and final temperatures of water as recorded by an observer are $(38.6 \pm 0.2){ }^{\circ} \mathrm{C}$ and $(82.3 \pm 0.3){ }^{\circ} \mathrm{C}$. The rise in temperature with proper error limits is

If $L$ is the inductance and $R$ is the resistance then the SI unit of $\frac{L}{R}$ is