Significant digits allow scientists to express data to the required degree of accuracy. Remember, the more decimal places a measurement has, the more accurate, or sensitive, the measurement is said to be.

Practice counting significant digits: significant digits practice worksheet

## Rules for Counting Significant Digits

**1. All non-zero numbers are significant.** (1, 2, 3, 4, 5, 6, 7, 8, 9, etc)

*Example:* 5.678 has four significant digits.

**2. Zeros within a number are always significant.** (Zeros that are sandwiched.)

*Example: *7.01 kilometers has three significant digits.

*Example: *2005.307 has seven significant digits.

**3. Zeros that do nothing but set the decimal point are not significant.** (Place holders)

*Remember the trick, if you can write the number in scientific notation then the zeros are most likely place holders. *

*Example: *100 has one significant digit. (100 = 1 x 10^2 | 1 is the significant digit.)

*Example: *0.0087 has two significant digits. (0.0087 = 8.7 x 10^-3 | 8 and 7 are the significant digits.)

**4. Trailing zeros that aren’t needed to hold the decimal point are significant.** (Zeros to the right of the decimal point)

*Example: *7.0 has two significant digits.

*Example: 3*.15000 has six significant digits.

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## Rules for Computing Significant Digits

### Addition and Subtraction with Significant Digits

### When measurements are added or subtracted, the answer can contain no more **decimal places** than the least accurate measurement.

### Multiplication and Division with Significant Digits

When measurements are multiplied or divided, the answer can contain no more **significant figures** than the least accurate measurement.

SOURCE:

“Significant Figures.” General Chemistry Topic Review, Purdue University College of Science Chemical Education Division Groups. Web. June 13, 2013.