Calculation methods used in our school today. A guide for Parents and Carers. This is the way we do...
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Transcript of Calculation methods used in our school today. A guide for Parents and Carers. This is the way we do...
Calculation methods used in our school today.
A guide for Parents and Carers.
This is the way we do it (or at least some of the ways).
“They didn’t do it like that in my day!”
• Partitioning
• Chunking
• Number line
• Grid multiplication
Which is more important?
Mental Calculations
Or
Written Methods
When faced with a calculation, no matter how large or difficult the numbers may appear to be,
all children should ask themselves:
Can I do this in my head?
If I can’t do it wholly in my
head, what do I need to write
down in order to help me
calculate the answer?
Do I know the approximate size of the answer?
Will the written method I know
be helpful?
Addition
• On a whiteboard do this sum – 343 + 579
• In your head work out £3.99 added to £4.56.
• How did you do it?
Adding – Informal Methods86 + 57
86 136 140 143
+50
+4 +3
143
+7
Moving to a column method.
625 + 148
625
13
+ 148700 60
600 + 10020 + 40
5 + 8
773
625
700
148 13 60 20 + 40
5 + 8
773
600 + 100
Using a Standard Method
587 + 475
587 + 475
7 + 5 = 12Place the 2 in the units column
and carry the10 forward to the
tens column.
21
6011
80 + 70 = 150 then + 10 (carried forward) which totals 160.
Place the 60 in the tens column and carry the 100 forward to the hundreds column.
500 + 400 = 900 then + 100 which totals 1000. Place this in the thousands column
Subtraction
• On a whiteboard do this sum: 601 - 456
• In your head work out how much change you get from £20.00 if you spend £14.75.
• How did you do it?
Subtraction – Taking AwayHow do the number line and the column method link?
586 600 900 954590
+4 +10 +300 +54
954 - 586 Find the difference between the two numbers.Count on from 586 to 954.
954-586
368
10
54
4
300
Count onto the next multiple of 10
Count onto the next multiple of 100
Count onto the larger number
Count on in 100’s
To make 590
To make 600
To make 900
To make 954
Multiplication
• On a whiteboard do this sum: 45 x 15
• In your head work out how much you would spend if you bought 5 rolls of wallpaper at £16.99
• How did you do it?
Multiplication Using a Number Line.
14 x 510 x 5
1 x 5
1 x 5
1 x 5
1 x 5
70656055500
Grid Multiplication
• Partitioning
• Splits a number into its parts (makes it easy to see)
• E.g. 14 x 5 = (10 x 5) + (4 x 5)
14 x 5 (in a grid)
x
7020505
10 4
But can be done with “long multiplication”?
x
12
40 6
80
1200 1380
2
18030
46 x 32
92
1472
Expanded Method and Compact Method (you might recognise this one)
46X 321200
121472
80
(40 x 30)
(40 x 2)(6 x 2)
(6 x 30)180
46
1380(46 x 2)
X 32(46 x 30)
921472
Division• On a whiteboard do this sum: 640 divided by 12
• In your head work out how many 20cm pieces of ribbon you can get from a 2.4m roll.
• How did you do it?
Introducing division with a number line.
29 divided by 5
0 5 10 15 20 25 29
4 left over
5 groups of 5 with 4 left over5 r 4 This can also
be donebackwards.
Chunking on a Number Line
72 divided by 5
722220
5 x 10Subtract 10 groups
Of 5 from 72 to land on 22
5 x 4Subtract 4 groups
Of 5 from 22 to land on 2
14 groups of 5 subtracted together
R22 left!
This is the remainder
14 r2
Turning this into a column
72
22
2
0
5 x 10
5 x 4
r2 72 div 5 = 14 r2
Chunking256 divided by 7
256
0
4
186
46
116
7 x 10
7 x 10
7 x 10
7 x 6
r4
36 r4
-70
-42
-70186
116
46-70
4
7
7 x 6
7 x 10
7 x 10
7 x 10
Subtractchunks of70 (7 x 10)
How manyGroups of 7
in 46?
Total the numbers of groups of 710 + 10 + 10 + 6 = 36 r4
256-210
-4246
7
4
7 x 30
7 x 6
When comfortable with this then
move onto compact method
256