Transcript estimating_a_calculation

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
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Nearest
Nearest
Nearest
Nearest
ten?
hundred?
thousand?
ten thousand?
Nearest ten pence
Nearest one pound
or even
smaller
How to round
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You need to identify each place value in
the number
Place value in our system
Thousands Hundreds Tens
3
4
5
Ones or units
6
How would you read this number?
Place value in our system
Thousands Hundreds Tens
3
4
5
Ones or units
6
Three thousand four hundred
fifty six
Place value in our system
Thousands Hundreds Tens
8
0
1
Ones or units
2
How would you read this number?
Place value in our system
Thousands Hundreds Tens
8
0
1
eight thousand twelve
Ones or units
2
There are
no
hundreds
Place value in money
sign tens ones
ten
one
pence pence
£ 2 0 . 1
2
There is
no ‘p’
here
Twenty pounds and twenty pence
Place value in money
ten
pence
4
one
pence
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
45
What value is the halfway point?
Forty five is the halfway point?
The halfway point between
one hundred and two hundred
100
200
150
What value is the halfway point?
One hundred fifty is the halfway point?
The halfway point between
eight and nine thousand
8000
9000
8500
What value is the halfway point?
Eight thousand five hundred is the halfway point?
The halfway point between seven
thousand five hundred and seven
thousand six hundred
7500
7600
7550
What value is the halfway point?
Seven thousand five hundred fifty is the halfway point?
The halfway point between
twenty and thirty pence
20 pence
30 pence
25p
What value is the halfway point?
Twenty five pence is the halfway point?
What is halfway between
these two sets of numbers?
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30 and 40
100 and 200
700 and 800
1000 and 1100
1500 and 1600
2000 and 3000
130 and 140
0 and 1
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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
55
Round 52 pence to the nearest 10
pence.
Is 52 pence closer to 50 pence or 60
pence?
In which half of the line ?
30 pence
40 pence
35
Round each of these to the nearest 10p
34p
37p
31p
36p
35p
In which half of the line ?
£3
£4
£3.50
Round each of these to the nearest £1
£3.34
£3.72
£3.05
£3.90
£3.50
In which half of the line ?
£40
£50
£45
Round each of these to the nearest £10
£43.34
£48.72
£44.05
£49.05
£43.50
Rounding to the nearest 10
without a number line
283 the answer is either 280 or 290
Round to 10 underline the tens place
Look at the digit to the right to decide
if it is a 5, 6, 7, 8 or 9 round up
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
Round to 10 underline the tens place
Look at the digit to the right to decide
if it is a 5, 6, 7, 8 or 9 round up
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
Round to 100 underline the hundreds
place
Look at the digit to the right to decide
if it is a 5, 6, 7, 8 or 9 round up
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
Round to 1 underline the ones place
Look at the digit to the right to decide
if it is a 5, 6, 7, 8 or 9 round up
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
Round to 10p underline the 10p place
Look at the digit to the right to decide
if it is a 5, 6, 7, 8 or 9 round up
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
Round to £1 underline the £1 place
Look at the digit to the right to decide
if it is a 5, 6, 7, 8 or 9 round up
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
….
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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
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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
….
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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
….
….