Counting & Rounding Off Significant Figures

Counting Significant Figures

When counting the number of significant figures in a measurement, the following rules apply

1. Non zero integers are always significant

Non zero integers are defined as all numbers that are not zero. In other words numbers 1-9.

For example: "19" = 2 significant figures

"451.3" = 4 significant figures

2. Zero integers come in the following three classes where

3. Exact numbers are always significant.

Exact numbers involve counting not measurement so there is no uncertainty

For example: 10 fingers (counting) = 2 significant figures but 10 cm (measurement) = 1 significant figure

100 dollars = 3 significant figures

3150 people = 4 significant figures

For the following problems, count the number of significant figures

1) 0.02 _____________ 6) 5,000. ________

2) 0.020_____________ 7) 6,051.00 _______

3) 501 _____________ 8) 0.0005 ________

4) 501.0 _____________ 9) 0.1020 ________

5) 5,000 _____________ 10) 10,001 ________

Click here for the answers

1. Underline the significant digit that needs to be rounded.

Example: Round the number below to 4 significant digits.

2. Draw a line to the right of the underlined digit to show where the number must be cut off.

3. If the neighboring number is equal or greater than 5, the preceding digit is increased by 1.

If the neighboring number is less than 5, the preceding digit remains the same.

Here are some examples of numbers that were rounded off to a certain number of significant figures

Try to fill out the following table rounding off to to correct number of significant figures