How do you evaluate significant figure?

Answer 1

A significant figure is a bit like a decimal place, in that just how a maths question may ask for the answer 'to 2 decimal places' it may also be answered to '2 significant figures'.

For example, say you have the answer: 3.1415926

To 1 decimal place it would be: 3.1

(because you round the 4 after the 1 down, because it is less than 5), because there is 1 digit after the decimal place (.)

To (a certain amount) of significant figures, however, means the total amount of digits/numbers in the answer, for example:

To 3 significant figures, the answer would be: 3.14 because there are now just 3 digits in the answer.

However, a '0' does not count as a significant figure if it is before/after a set of regular (1-9) numbers (but it does count if it is in-between).

For example: 0.00000454

This is still to 3 significant figures, because the '0's are before the other numbers, and so do not 'count'.

The same can be said for: 45400000000

This is still to 3 significant figures, because the '0's are after the other numbers, so they do not count.

However: 400045

This is NOT to 3 significant figures, because the '0's are IN BETWEEN the other numbers, and so they DO count as significant figures.

Hope I helped :)