Calculate the mean percentage error in five observations: $80.0, 80.5, 81.0, 81.5, 82.0$. (in $\%$)

$A$ public park,in the form of a square,has an area of $(100 \pm 0.2) \, m^2$. The side of the park is ......... $m$.

Two intervals of time are measured as $\Delta t_1 = (2.00 \pm 0.02) \ s$ and $\Delta t_2 = (4.00 \pm 0.02) \ s$. The value of $\sqrt{(\Delta t_1)(\Delta t_2)}$ with correct significant figures and error is

The resistance $R = V / I$ where $V = (100 \pm 5) \; V$ and $I = (10 \pm 0.2) \; A$. Find the percentage error in $R$. (in $\%$)

Mass and volume of a body are found to be $(6.00 \pm 0.03) \text{ kg}$ and $(2.00 \pm 0.02) \text{ m}^3$ respectively. Then the density of a body is

The measured value of the length of a simple pendulum is $20 \ cm$ with $2 \ mm$ accuracy. The time for $50$ oscillations was measured to be $40 \ s$ with $1 \ s$ resolution. From these measurements,the accuracy in the measurement of acceleration due to gravity is $N \%$. The value of $N$ is: