Rounding part two

The distance that we looked at from London to New York was 4558.8 miles. This number has 5 significant figures. Significant figures are the figures (or digits) that show how accurate a number has been stated. After we rounded it to 4559, it had 4 significant figures.

We are going to round it further. Let’s round the number to 3 significant figures. To do this, we do the same thing that we did when we were rounding to zero decimal places. We want to know if we should round 4559 to 4550 or 4560.

From the number line above, it is clear that 4559 is nearer to 4560 than 4550 and so we round it up to 4560.

If we are rounding to three significant figures, then we look at the fourth figure, if it is a 5 or higher, we round up. If it is a 4 or lower, we round down.

To tell your friend it is four thousand, five hundred and sixty miles is still very accurate. Let’s round 4560 to 2 sig fig (often sig fig is written instead of significant figures).

We need to check if the third figure is 5 and above or 4 and below. It is a 6, so we round up to 4600.

I would would be more likely to tell my friend that it is 4600 miles from London to New York than I would to say it is 4558.8 miles.

4600 is accurate to 2 sig fig.

4558.8 is accurate to 5 sig fig and to 1 decimal place.