# 3.2 Selection and computations

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## To describe observed relationships and rules in your own words [lo 2.2]

1. Look carefully at the following problems and explain to a friend what your approach would be in calculating the various answers.

1.1 $\frac{7}{8}-\frac{3}{4}$

1.2 $\frac{\text{11}}{\text{12}}-\frac{2}{3}$

1.3 $\frac{5}{6}-\frac{7}{\text{12}}$

1.4 $2\frac{1}{2}-1\frac{9}{\text{10}}$

1.5 $3\frac{1}{5}-1\frac{7}{\text{10}}$

1.6 $4\frac{1}{4}-2\frac{7}{8}$

Now calculate the answers.

## To describe observed relationships and rules in your own words [lo 2.2]

1. Sometimes one can use a pie graph to represent fractions. A survey was done of the extramural activities of a Grade 5 class and the results were represented by using a pie graph. See whether you can “read” it, and then complete the table.
 Activity Netball Tennis Rugby Choir Chess Swimming Fraction ........... ........... ........... ........... ........... ...........

2. It is important for us to be able to interpret the pie graph, otherwise we will not be able to make meaningful deductions from it and solve the problems. Work through the following problem with a friend and find out how many methods can be used to solve it.

If there are 50 learners in the class, how many learners play netball?

2.1 The question is $\frac{3}{\text{10}}$ of 50

$\frac{1}{\text{10}}$ of 50 = 5

$\frac{3}{\text{10}}$ of 50 will be 15

2.2 I must calculate $\frac{3}{\text{10}}$ of 50. I find out what $\frac{1}{\text{10}}$ is by dividing 50 by 10.

50 ÷ 10 = 5

If one tenth is 5, then 3 tenths will be 3 × 5. There are thus 15 pupils who play netball.

2.3 Girls = $\frac{3}{\text{10}}$ of 50

Thus: = (50 ÷ 10) × 3

= 5 × 3

= 15

2.4 $\frac{3}{\text{10}}$ of 50 = 3 × $\frac{1}{\text{10}}$ of 50

= 3 × 5

= 15

3. What would you say is the “rule” for these “of” sums?

4. Which of these methods do you prefer?

Why?

5. Look again at the methods at 2.1 and 2.2. What do you notice?

6. Can you say how many learners in Act. 2 participate in:

rugby?_______ ; swimming? _________

7 Now calculate:

7.1 $\frac{7}{\text{12}}$ of 36

7.2 $\frac{5}{8}$ of 32

7.3 $\frac{6}{7}$ of 350

7.4 $\frac{3}{4}$ of 224

Do you still remember?

1 000 m. = 1 litre

1 000 litre = 1 kℓ

1 000 g = 1 kg

1 000 kg = 1 t

1 000 mm = 1 m

1 000 m = 1 km

## To calculate through selection and by using suitable computations [lo 1.8.6]

1. Let us see whether you are able to successfully apply the knowledge that you have acquired up to now. Work on your own and calculate:

1.1 Five learners share 1 litre of cool drink equally. How many m $\ell$ does each learner get?

1.2 Zane lives 2 km from the school. He has already covered $\frac{3}{4}$ of the distance. How far has he walked? (Give your answer in m).

1.3 The mass of a bag of flour is 1 kg. Mom needs $\frac{3}{\text{10}}$ of this to bake a cake. How much flour will she use?

1.4 Joy buys 3 m of material but only uses $\frac{1}{6}$ of this to make a dress.

What fraction of material is left over?

How much material is left over?

## Activity 4:

• To use tables and graphs to arrange and record data [LO 5.3]
• To draw and interpret a graph [LO 5.5.1]

#### Questions & Answers

Do somebody tell me a best nano engineering book for beginners?
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
what is the Synthesis, properties,and applications of carbon nano chemistry
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
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
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
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
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.
how did you get the value of 2000N.What calculations are needed to arrive at it
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Berger describes sociologists as concerned with
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