Round off to 3 significant figures (a) 20.96 and (b) 0.0003125

Explanation

(i) 20.96 has four significant figures. The fourth significant figure is more than 5 and hence on rounding off to three significant figures, the given measurement will become 20.9 + 0.1 i.e., 21.0.
(ii) 0.0003125 has four significant figures. The fourth significant figure is 5 and hence on rounding off to three significant figures, the given measurement will become 0.000312 or `3.12 xx 10^(-4)`. This is because 2 before 5 is an even number.