How to round to one decimal place. (1 decimal place, 1dp)

You can’t really get by in math without being able to round off. In this article I will show you how to round a number off to 1 decimal place (or 1 d.p).

First of all you will need to remember the basic rules:

a) If the number is 5 or above round up – add 1 onto the last digit

b) If the number is less than 5 round down – keep the number the same

Rounding a number to 1 decimal place, means that you want your answer so that there is only one number after the decimal point.

Example 1

Round 164.38 to 1 decimal place.

First of all underline all the numbers up to 1 number after the decimal point.

164.38

Now, there are two possible answers. If you round the number down the answer is 164.3 (stays the same) or if you round the number up the answer is 164.4 (add 1 onto the last digit underlined)

To decide which answer we choose look at the number after the underlining (the 8)

Since the number is 8 we round up (since 8 is 5 or above)

So the answer is 164.4 (1 dp)

Example 2

Round 81.6245 to 1 decimal place.

First of all underline all the numbers up to 1 number after the decimal point.

81.6245

Now, there are two possible answers. If you round the number down the answer is 81.6 (stays the same) or if you round the number up the answer is 81.7(add 1 onto the last digit underlined)

To decide which answer we choose, look at the number after the underlining (the 2). All the numbers after the 2 (4 and 5) are irrelevant.

Since the number is 2 we round down (since 2 is less than 5)

So the answer is 81.6 (1 dp).

Example 3

Round 3.0584 to 1 decimal place.

First of all underline all the numbers up to 1 number after the decimal point.

3.0584

Now, there are two possible answers. If you round the number down the answer is 3.0 (stays the same) or if you round the number up the answer is 3.1 (add 1 onto the last digit underlined)

To decide which answer we choose, look at the number after the underlining (the 5). All the numbers after the 5 (8 and 4) are irrelevant.

Since the number is 5 we round up (since 5 is half way, and 5 or above you always round up)

So the answer is 3.1 (1 dp).

Example 4 (This one is tricky!)

Round 34.96 to 1 decimal place.

First of all underline all the numbers up to 1 number after the decimal point.

34.96

Now, there are two possible answers. If you round the number down the answer is 34.9 (stays the same) or if you round the number up the answer is 35.0 (add 1 onto the last digit underlined, so the 9 becomes 10 and you need to add the extra 1 to the units!)

To decide which answer we choose, look at the number directly after the underlining (the 6).

Since the number is 6 we round up.

So the answer is 35.0 (1 dp).

Remember to check out my other articles on rounding to other decimal places.

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