1.18 To perform mental calculations

Mathematics

Number concept

Educator section

Memorandum

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

Leaner section

Content

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?

What is your answer? __________________________________________________

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:

Do you still remember?

The answer to an addition sum is called the SUM.

Thus: 4 873 + 2 168 = 7 041

addend addend sum

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

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:

1.9.1: addition and subtraction.