Strategies2012

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?


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?


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?


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?


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?


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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Strategies2012