# Calculating percentage

```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
In both cases there were 40% girls. Does not mean it has the same number of girls. One class
We will all now turn to Chapter 15, page 140.
You will solve the Ex 15.3 B Q1 (all sub questions) to Q10 in your workbooks and send your work on
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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.