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• GETIntPhaseMaths

This module and collection are included inLens: Siyavula: Mathematics (Gr. 4-6)
By: Siyavula

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# To perform mental calculations

Module by: Siyavula Uploaders. E-mail the author

## Memorandum

1. 4

2.1 2 4

2.2 3 3

2.3 6 6

2.4 5 5

2.5 1 5

2.6 7 2

2.7 3 6

• Lets review

Difference

• Do you remember

Only 2 factors have/can only be divided by 1 and itself.

Always divisible by 2.

1. 13 – 7 5. 91 - 3

2. 31 – 3 6. 97 - 7

3. 53 – 5 7. 59 – 7

4. 71 – 11

## LEANER SECTION

### Activity: To perform mental calculations [LO 1.9.1]

1. How accurately can you still subtract? The grid contains a hidden number. Use the clues to colour in the blocks that will reveal the number.

1.1 14 – 9

1.2 17 – 8

1.3 21 – 7

1.4 23 – 6

1.5 20 – 12

1.6 42 – 13

1.7 45 – 18

1.8 39 – 16

1.9 34 – 15

1.10 104 – 7

1.11 106 – 8

1.12 103 – 8

1.13 101 – 5

 2 12 106 8 18 19 81 66 70 21 5 63 101 12 50 14 117 80 64 73 9 109 68 76 7 98 86 29 22 72 27 96 38 17 8 97 88 71 11 95 83 3

### What is the hidden number? ___________________________________________

2. More fun!

You must now think carefully. Do you still remember what the “inverse” of subtraction is? This may help us find the answer to subtraction sums quickly. Work with a partner and see who is the first one to identify the figure that is hidden behind each cloud!

#### Let's revise!

• Do you still remember?

The answer to a subtraction sum is called the .

The inverse of subtraction is

## Assessment

Learning Outcome 1:The learner will be able to recognise, describe and represent numbers and their relationships, and to count, estimate, calculate and check with competence and confidence in solving problems.

Assessment Standard 1.9: We know this when the learner performs mental calculations involving:

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##### Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

##### What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

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