Calculating a percentage of a quantity
Learning objectives:
21.1.2021
All Learners can calculate a given percentage of a quantity without using a calculator.
Most learners can use this knowledge to solve word problems
We all use Percentage in our common conversation. For example 40% of the students in class are
girls. Does that mean there are 40 girls? No it doesn’t, What is means is I first need to see how many
students are there in class. Let us consider a class of 30 students.
We can now say 40% of 30 is girls.
% - Per cent or per hundred.
Of – we all know this means x (times or multiply)
Hence 40 % can be written as 40 / 100
Now when I solve it, I can write is as
40 x 30
100
This is equal to 40 x 30 = 1200 divided by 100 which is 12.
We have without much difficulty found out that there are 12 girls in the class.
If 40 % are girls it also means that 60% are boys . Now let us do the same thing to find the number of
boys.
60% of 30 can be written as
60 x 30
100
This is equal to 60 x 30 = 1800 divided by 100 which is 18.
We have without much difficulty found out that there are 18 boys in the class.
We can also check if 12 + 18 = 30 (It is !!!)
Which means we know that there are 12 girls and 18 boys in this particular class.
It will change if the number of students changes.
Example 2
Let us consider a class of 20 students.
We can now say 40% of 20 is girls.
% - Per cent or per hundred.
Of – we all know this means x (times or multiply)
Hence 40 % can be written as 40 / 100
Now when I solve it, I can write is as
40 x 20
100
This is equal to 40 x 20 = 800 divided by 100 which is 8.
We have without much difficulty found out that there are 8 girls in the class.
If 40 % are girls it also means that 60% are boys. Now let us do the same thing to find the number of
boys.
60% of 20 can be written as
60 x 20
100
This is equal to 60 x 20 = 1200 divided by 100 which is 12.
We have without much difficulty found out that there are 12 boys in the class.
We can also check if 8 + 12 = 20(It is !!!)
Which means we know that there are 8 girls and 12 boys in this particular class.
What have we understood till here?
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Percent – means per Hundred
The total number for any given quantity (In the above case a class) makes a difference in the
answers.
In both cases there were 40% girls. Does not mean it has the same number of girls. One class
had 12 girls the other had 8.
We will all now turn to Chapter 15, page 140.
Your Task
You will solve the Ex 15.3 B Q1 (all sub questions) to Q10 in your workbooks and send your work on
Classdojo. You will upload it on your portfolio.
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You will copy the questions in your workbooks
You will show all the working exactly the way I have shown it
I am not there to check, but if you use a calculator 1) you will struggle in your examinations
and 2) I will be able to tell and wont be impressed.
You will upload your work by 22.01.2021 ( Tomorrow)
Thank you for your cooperation. Keep in touch if you have doubts ask for help (This what I am here
for ) and keep submitting your work in time 😊
Kind regards
Mrs Kanvinde.