Question

How many significant figures in the number 3.140

Enter -1 if the the number of significant figures is ambiguous

Answer 1

There are 4 sigfigs(significant figures).

All zeroes before a non-zero (0.001) are NOT sigfigs. There are none here, so disregard this for this situation.
All zeroes between ARE sigfigs, but again this is not significant(pun not intended).
Zeroes after non-zeroes depend on the decimal. The number 100 only has 1 sigfig, as the zeroes follow and there is no decimal at the end. This differs from the number 100., which has 3 sigfigs. The difference is the one has a decimal after the zeroes, meaning that it is more accurate. This rule also applies to a number such as 1.00, as here it has 3 sigfigs.

Since there are 3 non-zero numbers and one 0 after the decimal, there are (3 + 1) = 4 sigfigs.

I'm not sure if this is exactly right, but I'm pretty sure ,:)

Answer 2

In a number with decimal, zeroes to the right of last non-zero digit are significant.

Hence there are 4 significant digits in 3.140.

Hope this helps, have a great day ahead!