In this activity, we'll be **rounding whole numbers** to estimate the answers to addition questions.

**Estimating **can help us to decide if an answer to a problem is reasonable.

If our estimate and answer are very different, it is likely that we have made an error.

**Recap of rounding**

When rounding, we look at the digit to the right of the number we are rounding to.

If we are rounding to the nearest **10**, we look at the **ones** digit, if rounding to the nearest **100**, we look at the **tens** digit.

We round up or down depending on the value of this digit.

If this digit is** less than 5**, the number needs to be **rounded down.**

If this digit is **5 or above**, the number needs to be **rounded up.**

Let's have a look at some examples:

**What is 56 rounded to the nearest 10?**

When rounding to the nearest 10, we need to look at the digit in the **ones column**.

In 56, this is a 6, so we round up.

So 56 would be **rounded up **to 60

**What is 734 rounded to the nearest 100?**

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

There is a 3 in the tens column, so we round down.

734 would be** rounded down **to **700** because the tens digit is less than 5.

Note: The number rounds down to 700, not the previous 100 which would be 600!

Let's have a look at a question using rounding.

Estimate the answer to the addition by first rounding the numbers to the nearest ten.

27 + 32 =

We're rounding to the nearest 10, so we look at the digit in the** ones column.**

27 has a 7 in the ones column, so we **round up** to 30.

32 has a 2 in the ones column, so we **round down** to 30.

30 + 30 =** 60**

27 + 32 = 30 + 30 = 60

The actual answer is: 27 + 32 = 59

We can see that our answer is reasonable and probably accurate.

Now it's your turn to have a go at some questions using rounding to estimate answers.