Rounding to significant figures

The method of rounding to a significant figure is often used as it can be applied to any kind of number, regardless of how big or small it is. When a newspaper reports a lottery winner has won £3 million, this has been rounded to one significant figure. It rounds to the most important figure in the number.

To round to a significant figure:

  1. look at the first non-zero digit if rounding to one significant figure
  2. look at the digit after the first non-zero digit if rounding to two significant figures
  3. draw a vertical line after the place value digit that is required
  4. look at the next digit
  5. if it's 5 or more, increase the previous digit by one
  6. if it's 4 or less, keep the previous digit the same
  7. fill any spaces to the right of the line with zeros, stopping at the decimal point if there is one

Examples

Round 53,879 to 1 significant figure, then 2 significant figures.

  • 5|3879 to 1 significant figure is 50,000
  • 53|879 to 2 significant figures is 54,000

Notice that the number of significant figures in the question is the maximum number of non-zero digits in your answer.

Round 0.005089 to 1 significant figure, then 2 significant figures.

  • 0.005|089 to 1 significant figure is 0.005
  • 0.0050|89 to 2 significant figures is 0.0051
Question

What is 98,347 rounded to 1 significant figure, then 2 significant figures?

  • 9|8347 to 1 significant figure is 100,000
  • 98|347 to 2 significant figures is 98,000
Question

What is 3.5175 rounded to 1 significant figure, then 2 significant figures?

  • 3|.5175 to 1 significant figure is 4
  • 3.5|175 to 2 significant figures is 3.5