The values of a number of quantities are used in a mathematical formula. The quantity that should be most precise and accurate in measurement is the one

The random error in the arithmetic mean of $100$ observations is $x$; then the random error in the arithmetic mean of $400$ observations would be

Quantity $Z$ varies with $x$ and $y$ according to the equation $Z = x^2y - xy^2$,where $x = 3.0 \pm 0.1$ and $y = 2.0 \pm 0.1$. The value of $Z$ is:

Students $A, B$ and $C$ measure the length of a room using a $25 \,m$ long measuring tape of least count $0.5 \,cm$,a meter-scale of least count $0.1 \,cm$,and a foot-scale of least count $0.05 \,cm$,respectively. If the actual length of the room is $9.5 \,m$,which of the following students will report the lowest relative error in the measured length?

$A$ physical quantity $Q$ is related to four observables $a, b, c, d$ as follows: $Q = \frac{ab^4}{cd}$,where $a = (60 \pm 3) \ Pa$,$b = (20 \pm 0.1) \ m$,$c = (40 \pm 0.2) \ Nsm^{-2}$,and $d = (50 \pm 0.1) \ m$. The percentage error in $Q$ is $\frac{x}{1000}$,where $x = $ . . . . . . .

$A$ physical quantity $C$ is related to four other quantities $p, q, r$ and $s$ as follows:
$C = \frac{pq^2}{r^3 \sqrt{s}}$
The percentage errors in the measurement of $p, q, r$ and $s$ are $1\%, 2\%, 3\%$ and $2\%$ respectively.
The percentage error in the measurement of $C$ will be . . . . . . $\%$.