# 4.23 To do mental arithmetic

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## Memorandum

1. 6 × 7 = 42

2. 7 × 9 = 63

3. 6 × 7 = 42

4. 9 × 5 = 45

5. (4 × 12) + 13 = 61

6. (6 × 8 ) + 8 = 56

7. 144 ÷ 12 ÷ 6 = 2

8. 2 001 – 17 = 1 984

9. 72 ÷ 8 = 9

10. 24 ÷ 3 = 8

11. 132 ÷ 11 = 12

12. 3 × 3 × 3 = 27

13. 96 ÷ 12 = 8

14. ( 30 ÷ 6) × 4 = 20

15. 13 × 4 × 8 × 0 = 0

TEST

1.

1.1 straight angle

1.2 obtuse angle

1.3 acute angle

2.

• 40º
• 150º

3.

3.1 No

3.2 Yes

4. 8 ; 8 ; 6

5. The ages of ten teachers are as follows:

23 ; 23 ; 29 ; 35 ; 41 ; 42 ; 42 ; 42 ; 47 , 53

5.1 42

5.2 41 / 42

5.3 37 ,7

6. Total number of times it took place

Total number of posibilities

7.

7.1 $\frac{7}{\text{17}}$

7.2 $\frac{7}{\text{27}}$

## Activity: to do mental arithmetic [lo 1.9]

Let's round off the year's work with our last mental arithmetic test. Test your skill by answering the following questions as quickly and correctly as possible:

1. 6 × 7 = _____________________

2. 7 × 9 =_____________________

3. 6 × _____________________ = 42

4. _____________________ × 5 = 45

5. (4 × 12) + 13 = _____________________

6. (6 × _____________________) + 8 = 56

7. _____________________ ÷ 12 ÷ 6 = 2

8. 2 001 – 17 = _____________________

9. 72 ÷ _____________________ = 9

10. _____________________ ÷ 3 = 8

11. 132 ÷ 11 = _____________________

12. 3 × 3 × 3 = _____________________

13. 96 ÷ _____________________ = 8

14. (_____________________ ÷ 6) × 4 = 20

15. 13 × 4 × 8 × _____________________ = 0

TEST

1. What kind of angles are the following?

 1.1 1.2 ___________________________________ ______________________________ 1.3 ___________________________________ ______________________________

(3)

2. Measure the following angles with your protractor:

 2.1 2.2 ___________________________________ ______________________________

(2)

3. Do the following figures have rotational symmetry?

 3.1 3.2 ___________________________________ ______________________________

(2)

4. Complete: A cube has _______________ edges; ________________ angular

points and _________________________________ faces.

(3)

5. The ages of ten teachers are as follows:

35 ; 41 ; 23 ; 42 ; 42 ; 53 ; 47 ; 42 ; 23 , 29

5.1 Determine the mode:

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

(1)

5.2 Determine the median:

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

(2)

5.3 Determine the arithmetical average:

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

(3)

6. What “formula” is used to determine possibility?

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

(2)

7.

7.1 What is the probability that I will take a green ball out of a basket with 7 green, 6 red, and 4 yellow balls?

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

(1)

7.2 What is the probability that I will take a yellow Smartie from a container with

5 green, 9 blue, 7 yellow, 2 pink and 4 red Smarties?

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

(1)

## 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.

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