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

## 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]

what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
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.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
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
Do you know which machine is used to that process?
s.
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
how did you get the value of 2000N.What calculations are needed to arrive at it
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