# What is rounding numbers?

## What is rounding numbers?

## Rounding numbers to the nearest 10

A good way of explaining this is to use a number line.

If the **unit** of the number is **less than five**, the number needs to be **rounded down**.

If the **unit** of the number is **5 or above**, the number needs to be **rounded up**.

So 32 would be rounded down to 30, 35 would be rounded up to 40 and 38 would also be rounded up to 40:

## Rounding numbers to the nearest 100

If the **tens digit** is **less than 50** the **number is rounded down**.

If the **tens digit** is **50 or more**, the **number is rounded up**. (The units digit can be ignored when rounding a three-digit number to the nearest 100.)

So 834 would be rounded down to 800, 851 would be rounded up to 900 and 876 would be rounded up to 900:

## Rounding numbers to the nearest 1000

In **Year 4**, children need to **round four-digit numbers to the nearest ten, hundred or thousand**. Example questions may be as follows:

*What is 4231 rounded to the nearest ten? (Answer: 4230)*

What is 8163 rounded to the nearest hundred? (Answer: 8200)

What is 2839 rounded to the nearest thousand? (Answer: 3000)

Children are also expected to use their knowledge of rounding to **estimate answers to calculations** when checking their work.

For example: imagine a child has worked out 38 x 42 and got the answer 466.

In order to check if this is correct, it would be a good idea for them to round both 38 and 42 to the nearest ten and then multiply them, so the calculation they would do would be 40 x 40 = 1600. Although, 1600 is an approximate answer, it is completely different to 466 which means they would know that they had done something wrong in their initial calculating.

## Rounding decimal numbers

Children also need to round decimals in Years 4, 5 and 6. **In Year 4**, they will be introduced to rounding decimals with one decimal place to the nearest whole number. In **Year 5** they will move onto rounding decimals with two decimal places to the nearest whole number and to one decimal place. They may come across questions such as these:

What is 3.97 rounded the nearest whole number?(Look at the first number after the decimal point - 9. Because it is more than 5 you round the 3 to the left of it up to 4.) | Answer: 4 |

What is 8.42 rounded to one decimal place?(Look at the second digit after the decimal point - 2. Because it is less than 5, you leave the 4 to the left of it the same.) | Answer: 8.4 |

What is 3.928 rounded to two decimal places?(Look at the third digit after the decimal point - 8. Because it is more than 5, you round the 2 to the left of it up to 3.) | Answer: 3.93 |

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