Significant figures are mainly used in the field of science, such as chemistry. They are used to keep an unusual type of percision. Although sometimes things may become less accurate when using significant figures. "How do I know the number of significant figures in my measurement/number?" and "How do significant figures work in addition, subtraction, multiplication, and division?" will be answered shortly.

Determining the Number of Significant Figures for Numbers That Do Not Have Zeroes

Since no zeroes are involved,this is quite easy. Just count the number of digits, and you'll be fine. For example, 42 has two significant figures. 2.68957 has six significant figures. It's a bit tricky when zeroes enter the fray.

Rules for Determining Significant Zeroes

1. Zeroes that are in between nonzero digits are significant.

Example- 60.3 g has three significant figures.
94 003 L has five significant figures.

2. Zeroes that are in front of all nonzero digits are not significant.
Example- 0.037 914 m has five significant figures.
0.0003 kg has one significant figure.

3. Zeroes at the end of a number and to the right of the decimal point are significant.
Example- 21.00 dL has four significant figures.
7.000 000 000 km has ten significant figures.

4. The rules for rounding. These are not at all very difficult. If the first nonsignificant number is greater than five, the last significant number must be rounded up. If the first nonsignificant number is less than five, the last significant number must be rounded down. In the case of the first nonsignificant being five, different results may occur. When the five is proceeded by a number other than five, the last significant number must be rounded up. If a zero proceeds the five, and an odd preceeds the five, then the number is rounded up. If a zero proceeds the five, and the five is preceeded by and even (including the number zero), the number is rounded down.
3.678 becomes 3.68
2.941 becomes 2.94

5. Zeroes at the end of a number but to the left of a decimal point may or may not be significant. If a zero has not been measured or estimated but is just a placeholder, it is not significant.Example-It may actually be 9000 Tg, or the last two digits are unknown. A decimal point placed after zeroes indicates they are significant.
Example- 4900 Tg may contain from two to four significant figures, depending on how many zeroes are placeholders.
4900. Tg contains four significant figures, indicated by the presence of the decimal point.

Addition and Subtraction with Significant Figures

When your finished doing whichever operation, have the same number of digits to the right of the decimal point as the number that has the fewest nuber of digits to the right of the decimal point. And round your answer.
Example- 6.85 g + 2.1 g = 8.95 g then 9.0 g

Multiplication and Division with Significant Figures

The answer can have no more significant figures than are in the measurement with the fewest number of significant figures. Again, round your answer, please.
Example- 82.1 x 12 = 985.2 then 990