Least count \(=\frac{1}{20} cm -\frac{49}{50} \cdot \frac{1}{20} cm\)

\(=\frac{1}{50} \times \frac{1}{20} cm =0.01\,mm\)

\(\ln u =\ln h -\ln h ^{\prime}\)

\(\frac{ du }{ u }=\frac{ dh }{ h }-\frac{ dh ^{\prime}}{ h ^{\prime}}\)

\(du =\left[\frac{0.01}{5.25}+\frac{0.01}{5.00}\right] \frac{5.25}{5.00}\)

\(=\frac{41}{10} \times 10^{-3}\)

Ans. \(=41\)