**Year 3 Maths – Estimate Numbers ** *KS2 Revision*

## What you need to know

**Things to remember:**

- Estimating is just rounding
- If the units are 4 or less, we round down.
- If the units are 5 or more, we round up.
- We use estimates to see if our answer is close to the correct one.

Let’s have a look at some quick rounding questions.

**Number Rounded**

22 20

31 30

65 70

38 49

We will use estimating in a question like the following.

“Katie says that 16+31=77. Use estimate to see if she is correct.”

We will do this in two steps.

**Step 1:** Round both numbers

**Number Rounded**

16 20

31 30

**Step 2:** Add or subtract your numbers.

Katie was doing an addition, so we need to add these two numbers.

20+30=50

We can see that Katie’s answer should have been closer to 50, so she wasn’t right by saying 77. (The actual answer is 47).

Let’s see how we do it with subtraction. Find an estimation for the following subtraction:

55-28= \_\_

60-30= 30

So, we do it in the same way, we just have to subtract instead of add!

## Example Questions

**Question 1: **Find an estimate of the following addition:

23 + 62 = \_\_

Remember we need to round our numbers first.

Number Rounded

23 20

62 60

And then add them.

20 + 60 = 80

So, our estimate is 80.

**Question 2: **Find an estimate of the following addition:

76 - 13 = \_\_

Remember we need to round our numbers first.

Number Rounded

76 80

13 10

And then subtract them.

80 - 10 = 70

So, our estimate is 70.

Is this a good estimate?