3.2 Decimal fractions and rounding off

Mathematics

Decimal fractions

Educator section

Memorandum

• a) 41c

1. 42 $\frac{1}{2}$
2. 44c

• Rounding off

11.3.1 a) Look at the 2 ^nd digit after comma (100ths)

If 5, 6, 7, 8, 9: 10ths – digit 1 more

If 4, 3, 2, 1, 0: 10ths – digits remains the same

Replace everything after 10ths with noughts

1. Look at 3 ^rd digit after comma

If 5, 6, 7, 8, 9: 100ths – digit 1 more

If 4, 3, 2, 1, 0: 100ths – digit remains the same

Replace everything after 100ths with noughts

1. Look at 4 ^th digit after comma

If 5. 6, 7, 8, 9: Thousandths 1 more

If 4, 3, 2, 1, 0: Thousandths temain the same

Replace everything after 1 000ths with noughts

11.4 a) 4,5

9,9

5,3

7,6

52,6

88

11.4 b)

11.4 c) (i) (ii)

(iii) (iv)

• (vi)

12.2 a) 11

1. R406
2. 6
3. 5
4. R327
5. 8
6. 9
7. 14
8. 448
9. 1 390

Leaner section

Content

Activity: decimal fractions and rounding off [lo 1.4.2, lo 1.7.1]

11.1 DECIMAL FRACTIONS AND ROUNDING OFF

Work together with a friend. Look at the sketches. What does one potato cost in each case?

11.2 Round off the following to the nearest whole number. Write down the corresponding letter and see what word is hiding away.

a) 8,047

b) 15,51

c) 3,7

d) 35,236

e) 149,089

f) 6,4

g) 35,09

h) 38,456

i) 15,912

j) 236,199

k) 235,89

What is your answer? ...........................................................................

11.3.1 Work in groups of three. Formulate rules/methods for the following:

a) Rounding off to one decimal place (tenths):

b) Rounding off to two decimal places (hundredths):

c) Rounding off to three decimal places (thousandths):

11.3.2 Compare your answers with those of the rest of the class.

11.4

a) Complete the following flow diagram:

b) See if you can complete the table correctly:

c) Round off the following to 3 decimal places. Draw a circle around the correct answer:

12.1 Do you still remember?

1 000 ml = 1 litre

1 000 g = 1 kg

1 000 kg = 1 tonne

1 000 litres = 1 k

1 000 m = 1 km

100 c = R1,00

12.2 Fill in the missing answers:

e.g. 3 521 mm to the nearest m = 4 m

a) 11 296 mm to the nearest m = ......................... m

b) R406,38 to the nearest rand = R.........................

c) 6 455 litre to the nearest kl = ......................... kl

d) 4 823 kg to the nearest tonne = ......................... t

e) 32 687 c to the nearest rand = R.........................

f) 8 388 g to the nearest kg = ......................... kg

g) 8 630 m to the nearest litre = ......................... litres

h) 14 277 m to the nearest km = ......................... km

i) R4,4839 to the nearest cent = ......................... c

j) R13,9021 to the nearest cent = ......................... c

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 1.4 We know this when the learner recognises and uses equivalent forms of the rational numbers listed above, including:

1.4.2 decimals;

Assessment Standard 1.7: We know this when the learner estimates and calculates by selecting and using operations appropriate to solving problems that involve:

1.7.1 rounding off numbers to at least one decimal place.