Transcript Multiplication powerpoint KS2

Written Methods for
Multiplication in KS2
Firfield Primary School
Wednesday 25th November 2015
KS1 – Y3
• Mainly single digits x single digit
• Repeated Addition (4 x 6) = 6+6+6+6
• Children use a number line or beads to
support their understanding
• Use of inverse facts to complete number
sentences
• (? X 5 = 20)(3 x ? = 18) (? X ? = 32)
• Lots of times table practise and division
facts linked with them.
• Which leads us on to partitioning…
Hang on, what’s partitioning?
For bigger numbers (TU x U) we partition the
number into separate TENS and UNITS:
38 x 5 = (30 x 5) + (8 x 5)
= (150) + (40) = 190
38 x 5 = 30 x 5 = 150 (3 x 5 = 15 so 30 x 5 = 150)
8 x 5 = 40
30
8
Grid Method (TU x U)
•
•
•
•
A more formal way to set things out
Makes links to x by a multiple of 10
38 x 7 = (30 x7) + (8 x7) = 210 + 56 = 266
Estimate first (approx. 40 x 7 = 4 x 7 x 10)
X
7
30
210
8
56
266
Grid Method (TU x TU)
• Same as previous method
• Now with extra boxes!
• 72 x 38 (approx. 70 X 40 = 2800)
x
30
8
70
2100
560
2660
2
60
16
76
Use column addition method to total = 2736
Short Multiplication (x U)
• The one the adults in the room recognise!
• Initially emphasise the place value and
partitioning skills from previous methods.
• Multiply UNITS first then TENS…
3 8
X 7
266
5
Short Multiplication (X TU)
• Expanded to Multiply by Tens and Units
• Remember the zero (when x10)
1
2
2
X
1
1 4
2 4
3 8
4
6
4
0
4
2
1 2
x 2
74
2 4 8
3 2 2
1
4
6
4
0
4
Remember
• Children will be taught a range of calculation methods
(mental and written).
• Children will choose different methods depending on the
task.
• Children will not move on to the next stage if:
• They are not ready
• They are not confident
• Once children are using concise methods they will not go
back to expanded methods.
• Children should be encouraged to estimate answers
• Children should be encouraged to check their answers
using inverse operations or simple re-calculating.
• Children should consider when mental calculations are
more appropriate
How you can help
• Regular practise of times tables
• Know square numbers, doubles, x 10
• Explaining how to multiply any number by 10, 100 or
1,000 by showing how digits move to the left.
• By showing the links between x table facts such as:
5 x 6 = 30 so 5 x 60 = 300 or 50 x 60 = 3,000
• By showing partitioning and explaining place value
• Regular practise of written methods now that you
understand how to use them! (use it or lose it)
• Regular mental calculations that rely on partitioning
and an understanding of place value (what’s 42 x 5?)
(40 x 5 + 2 x 5 = 4 x 5 =20 so 40 x 5 =200 + 2 x 5 = 210)