Rules for Counting Significant Figures

When measuring to find a value, all absolutely known digits are significant plus one estimated digit. When looking at a value measured by somebody else:

- All non-zero digits are significant.
- All zeros between non-zero digits are significant.
- Leading zeros are never significant.
- Trailing zeros are typically considered significant when a decimal point is explicitly present. For our class, we will ALWAYS consider trailing zeros to be significant when a decimal point is explicitly present.
- Trailing zeros are not typically considered significant when a decimal point is not present, but you can't be sure. For our class, we will NEVER consider trailing zeros to be significant when a decimal point is not explicitly present.
- When a number is expressed using scientific notation, all digits before the exponential factor are considered significant.
- Any absolute number is considered to have an infinite number of significant figures. For instance, there are EXACTLY six people in my immediate family. There is absolutely no uncertainty in the number of people in my family (there could not possibly 6.2 people or 5.7 people, for instance). So, the number of people in my family is considered to have an infinite number of significant figures.

Now, use the rules above to count significant figures in the self-quiz below. Good luck!

## Counting Significant Figures

### Self-Quiz

- How many significant figures are in the following number? 4.200 x 10^4
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- How many significant figures are in the following number? 2.300
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- How many significant figures are in the following number? 0.0004
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- How many significant figures are in the following number? 0.0470
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- How many significant figures are in the following number? 7500.0
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- How many significant figures are in the following number? 3.88 x 10^-3
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- How many significant figures are in the following number? 4.200 x 10^4
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- How many significant figures are in the following number? 500.
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