Q: Which of the following length measurement is most accurate and why ?

(i) 4.00 cm (ii) 0.004 mm (iii) 40.00 cm

Sol: $\frac{\Delta x}{x} = \frac{0.01}{4.00} = 0.0025 $

(ii) $\frac{\Delta x}{x} = \frac{0.001}{0.004} = 0.25 $

(iii) $\frac{\Delta x}{x} = \frac{0.01}{0.004} = 0.00025 $

The last observation has least fractional error and hence it is most accurate .