Rounding off decimals

In this section we shall be exploring rounding off decimals. We shall look at rounding decimals off to whole numbers, rounding decimals to certain decimal places and making decisions whether to round up or down decimals.

Rounding to the nearest whole number

Here is an example of rounding decimals to the nearest whole number;

Example

Round 7.3 to the nearest whole number.
We realise that this decimal number lies between 7 and 8. The following diagram shows where this decimal number is located between 7 and 8.

The number 7.3 has been shown on the number line above and the location where it’s located. We see that 7.3 is closest to 7, which means 7.3 to the nearest whole number is 7. This is the answer we’re after.

Round to one decimal place

In the following example we’re going to look at how to round to one decimal place.

Example

Round 2.37 to 1 decimal place.
The decimal number in question lies between 2.3 and 2.4 as shown below on the number line.

We can see that the number shown on the number line is closer to 2.4. Which means 2.37 to 1 decimal place is 2.4. This is the answer we have been searching for.

Between .5

You will usually have to work with numbers ending .5 to round off to a certain accuracy or decimal place, for example rounding off numbers such as 3.5, 4.5, 7.5, 8.5, 10.5, and 20.5 to the nearest whole number. Here is an example of rounding off .5 numbers.

Example

Round 4.5 to the nearest whole number.
The number 4.5 lies between 4 and 5 as shown below on the number line.

On the number line we can see that the number lies right in the middle of the number line between 4 and 5. Whenever it’s in the middle we always round up. So 4.5 to the nearest whole number is a 5. That’s the answer we have been looking for.