Mental Addition and Subtraction

​Mental addition & subtraction

Exercise 1C​

​Exercise 1C

​Consider:

98 +22 - 31 + 29​

​

Now write down the steps you took to work out your answer.​

​

​Exercise 1C

​Consider:

98 +22 - 31 + 29​

​

Now write down the steps you took to work out your answer.​

​

​Exercise 1C

​Consider:

98 +22 - 31 + 29​

​

Compare your answer to the person next to you

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​The order of numbers does not matter.

​

a + b = b + a

​

For example: 4 + 3 = 3 + 4​

​​Communicative Law

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​The pair that is added first does not matter

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a + (b + c) = (a + b) + c

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For example: 4 + (3 + 2) = (4 + 3) + 2

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​​Associative Law

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Poll

Consider your process from the first question, what type of strategy did you use?

• Partitioning

• Compensating

• Halving/doubling

• Other

​Your turn

Exercise 1C

Multiple Choice

State the sum of 19 and 8

• 11

• 28

• 27

• 29

Multiple Choice

Using the partitioning method, evaluate 132 + 156

• 298

• 286

• 256

• 288

Multiple Choice

Using the compensation method, evaluate 25 + 19

• 46

• 44

• 45

• 49

Multiple Choice

Using the compensation method, evaluate 56 - 18

• 46

• 38

• 48

• 35

Fill in the Blanks

Using the doubling/halving method, evaluate 35 + 36