# 1.18 To perform mental calculations

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1. 62; 63

2.1 9

2.2 132

2.3 17

2.4 331

2.5 498

2.6 68.5

2.7 1 000

2.8 144

2.9 +

2.10 10

2.11 63

2.12 176

2.13 7

2.14 4

2.15 450

## Activity:to perform mental calculations [lo 1.9.1]

1. See how many figures you can find in this garden and then add them together. If you work cleverly you will be able to calculate the answers in a flash! Are you able to see how?

2. Now we are going to test your mental calculation skills in a different way. If you know your multiplication tables and can also add and subtract well, you will not have any trouble. Try to complete these within three minutes:

2.1 ___________ x 8 = 72

2.2 ___________ ÷ 11 = 12

2.3 119 + ____________ = 136

2.4 _____________ - 214 = 117

2.5 Double 249: _________________

2.6 Halve 137: __________________

2.7 30 x _______________ = 30 000

2.8 4 x 3 x 12 = _______________

2.9 567 ______________ 23 = 590

2.10 8 670 ÷ _____________ = 867

2.11 (5 x 9) + 18 = _____________

2.12 (7 + 15) x 8 = ______________

2.13 (42 ÷ ___________) + 14 = 20

2.14 (5 x ______________) – 9 = 11

2.15 Halve x _________________ = 225

Complete by colouring in the appropriate block:

 I did WELL AVERAGE POORLY

## Do you still remember?

Thus: 4 873 + 2 168 = 7 041

3. Some more mental calculation!

Calculate the answers without using a calculator. Use the code and complete the following sentence:

Subtraction is called the _____________________________________ of addition.

3.1 27 + 35

3.2 48 + 16

3.3 53 + 19

3.4 23 + 37

3.5 39 + 17

3.6 15 + 24

3.7 26 + 34

 I A N K V O E 62 74 64 102 72 88 60
 B R Y S P M T 31 56 20 39 99 52 32

We can also say that subtraction is the in verse operation of addition. I can test an addition sum by subtracting.

## 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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