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8+5 =
9+8 =
I count up to 8 in my head then count on 9, 10, 11, 12, 13
I get 8 counters and 5 more
counters then count them all.
8 + 2 = 10 so 10 + 3 is 139 + 1 is 10 so 10 + 7 is 17
I count on from the biggest
number.So I go 9… 10, 11, 12, 13, 14, 15, 16, 17, 18
8 + 8 is 16 then add 1 OR
9 + 9 is 18 then takeaway 1
There are 36 people on the bus. 9 more people get on the bus.
How many people are there altogether on the bus?
What strategies would you use to solve this problem?
36+9 =
If you add 4 onto 36 you get 40 then you add on the other 5 to get 45 people on the bus
I counted on from 36 using my fingers and
got to 45.
Add on 10 then takeaway 1.
When you add on 10 you get 46 then you
need to takeaway 1 to get 45.
I know that 6 plus 9 is 15, so 30 + 15 is 45.
I know 6 + 6 is 12 so 36 + 6 = 42. Then add on the 3 more to get 45.
Te Kaha has 47 marbles. He plays Stacey and loses 8 marbles to Stacey.
How many marbles is Te Kaha left with?
What strategies would you use to solve this problem?
I compensated:47 – 10 = 37 37 plus 2 = 39
If I split 8 into 7 and 1, so I can do
47 – 7, which equals 40, then I only have to take away one more, which equals 39!
47 – 8 =
I used an open number line!
47
-7
+20
39
-1
40
I used balancing.47 – 8 =
49 – 10 = 39
+2 +2
Number Strategies
There are 53 people on the bus.29 people get off.
How many people are left on thebus?
What strategies would you use to solve this problem?
I used tidy numbers:
53 – 30 = 23 23 plus 1 = 24
I used balancing.53 – 29 =
54 – 30 = 24
I think of 53-29
3 – 9 I can’t do so I borrow a ten. 13 – 9 = 4.4 tens – 2 tens = 20.It’s 24.
I used an open number line!53 – 29 =
29 53
+20
+2030
+3+1
50
+1 +1
I used place value53 – 20 = 33. Minus another 9. Split the 9 into 3 and 6.33 - 3 = 30 so 30 – 6 = 24
Number Strategies
There are 47 children in the hall. 28 more children arrive.
How many children are in the school hall now?
What strategies would you use to solve this problem?
Four rows of ten is 40 and two rows of ten is 20, so 40 + 20 = 60 with 7 and 8 left! Double 7 = 14 plus 1 = 15
so there are 75 children.
I used tidy numbers:
50 + 28 = 7878 - 3 = 75.
I know that 50 plus 30 is 80 and 3 plus 2 is 5, so 80 - 5 is 75.
I think of 47+28
7 plus 8 is 15, so that’s 5 and carry one. 4
plus 2 is 6 plus one more ten is 7. so the answer
is 75.
I use an open number line!
47
75
+3+20 +5
47 + 28 =
Number Strategies
8 + 5 =
9 + 8 =
Make sense of these strategies
I count up to 8 in my head then count on 9, 10, 11, 12, 13
I get 8 counters and 5 more
counters then count them all.
8 + 8 is 16 then add 1 OR9 + 9 is 18 then takeaway
1
I count on from the biggest
number.So I go 9… 10, 11, 12, 13, 14, 15, 16, 17, 18
8 + 2 = 10 so 10 + 3 is 139 + 1 is 10 so 10 + 7 is 17
8 + 5 =
9 + 8 =
Number Strategies
I have $387 in my savings account.
I decide to buy a small TV for my bedroom and it costs $193.
How much money do I have left?
What strategies would you use to solve this problem?
I used my doubles. Double 190 is 380. So double 193 is
386 plus 1 more to get 194.
I use balancing.387 – 193 =
384 – 190 = 194
“I think of 387-193
7- 3 is 4. 8 – 9 I can’t do so I borrow a hundred. 180 – 90 = 90.200 – 100 is 100. It’s 194.
“I use an open number line!”387 - 193 =
193 387
+100+
20200
+87+7
300
-3 -3
I rounded up to 390 and takeaway 190 to get 200. then I need to take away the 3 I added on plus the other 3 so its 194.
I have a 6.3m length of fabric.
I used 3.75m to make a coat. How much fabric have I got
left?
What strategies would you use to solve this problem?
Number Strategies
What visual supports could
you use to support these
strategies?
What knowledge do students
require to solve problems at this
level?
“I used an open number line!”
6.3 – 3.75 =
3.75 6.3
+2
+20 4
+0.3
+0.25
6
6.3 – 2.3 = 4 4 – 0.25 = 3.75 so 2.3 + 0.25 = 2.55m
Addition and Subtraction StrategiesCounting allCounting on/back___________________________Using one fact to derive another
Near-doublesMaking tensUsing fivesKnown multiple facts
PartitioningStandard place value partitioningRounding & compensatingThrough the tens
ReversibilityEqual additionsCommutativeAveragingEquivalency
Counting
Part-whole
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