# 3.2 Decimal fractions and rounding off

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## 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)

 6,41 8,60 7,26 9,49 5,03 6,29

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

## 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.

 B D E F G I K 39 149 7 236 38 6 17
 L M N O R S T U 237 15 35 16 8 150 3 4

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:

 Number 4,368 6,411 8,599 7,255 9,493 5,034 6,286 Rounded off to 2 decimal places 4,37 ............. ............. ............. ............. ............. .............

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.

#### Questions & Answers

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Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
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what's the easiest and fastest way to the synthesize AgNP?
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abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
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Yasmin
what is the function of carbon nanotubes?
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I'm interested in nanotube
Uday
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what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
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silver nanoparticles could handle the job?
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Azam
Hello
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I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Mathematics grade 7. OpenStax CNX. Sep 16, 2009 Download for free at http://cnx.org/content/col11075/1.1
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