30.900 has 5 significant figures.
In 30900 there are [at least] three significant figures.
3.
There are three.
There is one significant digit in the number 10, as written.
30.900 has 5 significant figures.
In 30900 there are [at least] three significant figures.
3.
There are three.
There is one significant digit in the number 10, as written.
One of them.
Three significant figures. The two zeroes after the digit 5 are irrelevant.
Five. Count from the first nonzero digit to the last nonzero digit.
5. Count the number of digits from the first non-zero digit to the last non-zero digit.
Two. Although there is no way to be sure that the number is not accurate to the unit's digit.
The number whose farthest right significant digit determines it. Whatever place that digit is in is the last significant digit in the sum. For example: 433 + 150 + 3.67 + 8000 = 8586.67, but in sig figs this is only 9000, as the thousands digit is the lowest digit that can be represented.
Six: every digit from 6 onwards.