08/01/21

We are going to continue to look at rounding today. 

Today we are going to use rounding to help us to estimate the answer of a question.

Key To Rounding (rule 3)!!

If the number in the column you are looking at is:

1,2,3 or 4 you round DOWN

5,6,7,8,9 you round UP

First have a look at this question. 

We will now discuss how to estimate using rounding.

First lets take the Handbag

The handbag costs £58. So now we need to round 58 to the nearest 10. When rounding to 10 we need to look at the ones column. What number is in the one?

8 - So this means we would round up to the next 10.

£58 rounded to the nearest 10 = £60

Lets do the same for the other 2 items

The shoes cost £73. So now we need to round 73 to the nearest 10. Look at the ones column. What number is in the one?

3 - This means we would round down to the previous 10.

£73 rounded to the nearest 10 = £70

Lastly, the dress costs £35. So now we need to round 35 to the nearest 10. What number is in the one?

5 - This means we would round up to the next 10.

£35 rounded to the nearest 10 = £40

Now we have all 3 rounded numbers this makes a simple addition calculation

£60 + £70 + £40 = ?

All 3 items cost approximately £170

This is how we can use estimating to help us answer a question.

Lets have a look at the following 2 questions together.

First lets look at Elliott's method.

Lets start by rounding 642 to the nearest 10.

Look at the ones. > 2

Do we round up or down? Down

642 rounded to the nearest 10 = 640

Now lets round 93 to the nearest 10.

Look at the ones. > 3

Do we round up or down? Down

642 rounded to the nearest 10 = 90

640 + 90 = 730

Now lets look at Hannah's method.

Lets start by rounding 472 to the nearest 10.

Look at the ones. > 2

Do we round up or down? Down

642 rounded to the nearest 10 = 470

Now lets round 128 to the nearest 10.

Look at the ones. > 8

Do we round up or down? Up

642 rounded to the nearest 10 = 130

470 - 130 = 340

Now go onto Purple mash and complete the 2do for maths.