0.004207 round off to 3 significant figures

0.00421

Explanation:

Significant figures:

The given measurement have four significant figures 1234.

All non-zero digits are consider significant figures like 1, 2, 3, 4, 5, 6, 7, 8, 9.

Leading zeros are not consider as a significant figures. e.g. 0.03 in this number only one significant figure present which is 3.

Zero between the non zero digits are consider significant like 104 consist of three significant figures.

The zeros at the right side e.g 2400 are also significant. There are four significant figures are present.

In given value the 0.00 are not significant.

when we round to three significant figures we must include 4207. The number after the third significant figure which 7 is greater than 5 so we will increase the third significant figure by one for example 0 become 1.

If the number which is next to rounded figure is 5 or grater than five the rounded figure will increase by 1.

i do not get it   at all