It can be useful to **estimate** the answer to a question.

We often do this to see if the actual answer is likely to be correct - the estimation should be quite close to the answer.

We can use **rounding **to help us make a good estimation of an answer.

Some numbers need to be **rounded up** and others need to be **rounded down.**

**Rounding to the nearest ten:**

If a two-digit number ends in 5 or above, it **rounds up** to the next ten (3**5 **rounds up to 40).

If a two-digit number ends in 4 or below it **rounds down** to the previous ten (3**2 **- rounds down to 30).

**Rounding to the nearest hundred:**

When rounding to 100, we look at the digit in the tens column.

If it is 5 or above, we **round up** (3**6**7 - rounds up to 400).

If it is 4 or below, we **round down** (3**4**5 - rounds down to 300).

**I**f we are rounding to the nearest **1,000**, we would look at the digit in the **hundreds** column.

If we are rounding to the nearest **10,000,** we would look at the digit in the **thousands **column.

Can you see the pattern? We look at the column to the right of the digit we are rounding to!

**Example 1**

Estimate the answer to the following sum by rounding the numbers to the nearest hundred and then adding.

**453 + 326 **

4**5**3 **rounds up** to 500

3**2**6 **rounds down** to 300

Now add the numbers 500 + 300 = 800

The actual answer is 453 + 326 = 779 (a very close estimate).

**Example 2**

Estimate the answer to the following by rounding the numbers to the nearest t**en** and then **subtracting**.

**65 - 41**

6**5** rounds **up** to 70

4**1** rounds **down** to 40

Now subtract 70 - 40 = 30

The actual answer is 65 - 41 = 24 (a good estimate).

Are you ready to try some questions now?