The internal and external radii of a hollow cylinder are measured with the help of a vernier callipers.Their values are $(4.23 \pm 0.01)\,\,cm$ and $(3.87 \pm 0.01)\,\,cm,$ respectively. The thickness of the wall of the cylinder is

The least count of a stop watch is $\frac{1}{5}$ second. The time of $20$ oscillations of a pendulum is measured to be $25$ seconds. The maximum percentage error ig the measurement of time will be ..... $\%$

The radius of a sphere is measured to be $(7.50 \pm 0.85) \,cm .$ Suppose the percentage error in its volume is $x$. The value of $x$, to the nearest integer is .....$\%$

The percentage errors in quantities $P, Q, R$  and $S$  are $0.5\%,\,1\%,\,3\%$  and  $1 .5\%$ respectively in the  measurement of a physical quantity $A\, = \,\frac{{{P^3}{Q^2}}}{{\sqrt {R}\,S }}$ . the maximum percentage error in the value of $A$  will be ........... $\%$

A physical quantity $X$ is given by $X = \frac{{2{k^3}{l^2}}}{{m\sqrt n }}$ The percentage error in the measurements of $k,\,l,\, m$ and $n$ are $1\%, 2\%, 3\%$ and $4\%$ respectively. The value of $X$ is uncertain by .......... $\%$

What is estimation of error ? Write method for estimation.