$A$ force $F$ is applied on a square plate of length $L$. If the percentage error in the determination of $L$ is $3 \%$ and in $F$ is $4 \%$, then the permissible error in the calculation of pressure is (in $\%$)

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

In an experiment for determination of the focal length of a thin convex lens,the distance of the object from the lens is $10 \pm 0.1 \text{ cm}$ and the distance of its real image from the lens is $20 \pm 0.2 \text{ cm}$. The error in the determination of focal length of the lens is $n \%$. The value of $n$ is. . . . . . .

When two resistors of resistances $R_1=(200 \pm 2) \Omega$ and $R_2=(400 \pm 4) \Omega$ are connected in series,then the equivalent resistance of the combination is

The outer and inner radii of a hollow cylinder are $(4.23 \pm 0.01) \text{ cm}$ and $(3.89 \pm 0.01) \text{ cm}$ respectively. What is the thickness of the wall of the cylinder?

The density $\rho$ of a uniform cylinder is determined by measuring its mass $m$, length $l$ and diameter $d$. The measured values of $m, l$ and $d$ are $97.42 \pm 0.02 \text{ g}$, $8.35 \pm 0.05 \text{ mm}$ and $20.20 \pm 0.02 \text{ mm}$, respectively. The calculated percentage fractional error in $\rho$ is . . . . . . . (in $\%$)