Estimating a Calculation – use it when you don’t want an exact answer

Estimation is used when you want a rough or approximate idea for the answer to a sum

First step is to round all the numbers in the sum

Nearest ten? Nearest hundred? Nearest thousand? Nearest ten thousand? Nearest ten pence Nearest one pound

or even smaller

How to round

You need to identify each place value in the number

Place value in our system

Thousands

Hundreds

Tens Ones or units

3 4 5 6

How would you read this number?

Place value in our system

Thousands

Hundreds

Tens Ones or units

3 4 5 6

Three thousand four hundred fifty six

Place value in our system

Thousands

Hundreds

Tens Ones or units

8 0 1 2

How would you read this number?

Place value in our system

Thousands

Hundreds

Tens Ones or units

8 0 1 2

eight thousand twelveThere are no

hundreds

Place value in money

sign tens

ones

ten pence

one pence

£ 2 0 . 1 2

Twenty pounds and twenty pence

There is no ‘p’ here

Place value in money

ten pence

one pence

4 3 p

Forty three pence

There is no ‘£’ here

How to round

Now that you have identified each place value,

you need to identify the halfway point

The halfway point between forty and fifty

40 50

What value is the halfway point?

45

Forty five is the halfway point?

The halfway point between one hundred and two hundred

100 200

What value is the halfway point?

150

One hundred fifty is the halfway point?

The halfway point between eight and nine thousand

8000 9000

What value is the halfway point?

8500

Eight thousand five hundred is the halfway point?

The halfway point between seven thousand five hundred and seven thousand six hundred

7500 7600

What value is the halfway point?

7550

Seven thousand five hundred fifty is the halfway point?

The halfway point between twenty and thirty pence

20 pence 30 pence

What value is the halfway point?

25p

Twenty five pence is the halfway point?

What is halfway between these two sets of numbers? 30 and 40 100 and 200 700 and 800 1000 and 1100 1500 and 1600 2000 and 3000 130 and 140 0 and 1

35 150 750 1050 1550 2500 135 0.5

Did you notice that

there is a five in each of these

numbers?

How to round

Now that you’ve identified each place value and the halfway point -

you have to decide in which half of the line your number is in

In which half of the line ?

50 pence 60 pence

Round 52 pence to the nearest 10 pence.

Is 52 pence closer to 50 pence or 60 pence?

55 This half

Or this half?

In which half of the line ?

30 pence 40 pence

Round each of these to the nearest 10p

35 This half

Or this half?

34p 37p 31p 36p 35p

In which half of the line ?

£3 £4

Round each of these to the nearest £1

£3.50 This half

Or this half?

£3.34 £3.72 £3.05 £3.90 £3.50

In which half of the line ?

£40 £50

Round each of these to the nearest £10

£45 This half

Or this half?

£43.34

£48.72 £44.05

£43.50£49.05

Rounding to the nearest 10 without a number line

283 the answer is either 280 or 290

if it is a 5, 6, 7, 8 or 9 round up

Round to 10 underline the tens place

Look at the digit to the right to decide

if it is a 0, 1, 2, 3 or 4 round down

Rounding to the nearest 10 without a number line

8 the answer is either 0 or 0

if it is a 5, 6, 7, 8 or 9 round up

Round to 10 underline the tens place

Look at the digit to the right to decide

if it is a 0, 1, 2, 3 or 4 round down

Rounding to the nearest 100 without a number line

455 the answer is either 400 or 500

if it is a 5, 6, 7, 8 or 9 round up

Round to 100 underline the hundreds place

Look at the digit to the right to decide

if it is a 0, 1, 2, 3 or 4 round down

Rounding to the nearest 1 without a number line

1.8 the answer is either 1 or 2

if it is a 5, 6, 7, 8 or 9 round up

Round to 1 underline the ones place

Look at the digit to the right to decide

if it is a 0, 1, 2, 3 or 4 round down

Rounding to the nearest 10p without a number line

£0.08 the answer is either 0p or 10p

if it is a 5, 6, 7, 8 or 9 round up

Round to 10p underline the 10p place

Look at the digit to the right to decide

if it is a 0, 1, 2, 3 or 4 round down

Rounding to the nearest £1 without a number line

£2.05 the answer is either £2 or £3

if it is a 5, 6, 7, 8 or 9 round up

Round to £1 underline the £1 place

Look at the digit to the right to decide

if it is a 0, 1, 2, 3 or 4 round down

When rounding to the nearest ten – these are possible answers

00 10 20 30 40

50 60 70 80 90

100 110 120 130 140

150 160 170 180 190

200 210 220 …. ….

When rounding to the nearest 100 – these are possible answers

0 100 200 300 400

500 600 700 800 900

1000 1100 1200 1300 1400

1500 1600 1700 1800 1900

2000 2100 2200 …. ….

When rounding to the nearest 10 pence – these are possible answers

0p 10p 20p 30p 40p

50p 60p 70p 80p 90p

£1.00 £1.10 £1.20 £1.30 £1.40

£1.50 £1.60 £1.70 £1.80 £1.90

£2.00 £2.10 £2.20 …. ….

When rounding to the nearest £1 – these are possible answers

£0 £1 £2 £3 £4

£5 £6 £7 £8 £9

£10 £11 £12 £13 £14

£15 £16 £17 £18 £19

£20 £21 £22 …. ….

When rounding to the nearest £10 – these are possible answers

£0 £10 £20 £30 £40

£50 £60 £70 £80 £90

£100 £110 £120 £130 £140

£150 £160 £170 £180 £190

£200 £210 £220 …. ….