In this table we have two rows.
In one we will have the class interval,
which will be the price range of pens and in the second,
we will have the frequency, that is the number of pens sold of each range.
So these are the different class intervals that are given.
The first range is pens that cost between 10 and 20 rupees.
We can see that the upper limit of one interval
is equal to the lower limit of the next interval
making it continuous.
As It's continuous the first group would mean
10 rupees is less than,
or equal to the price of the pen which will be less than 20 rupees.
The lower limit is included, but the upper limit is not.
So in the second group 20 is included,
along with all numbers less than 30 but not equal to 30.
In the second row, we have the number of pens sold for each category.
15 pens of this category was sold, 20 of this category and so on...
Until now, we have seen examples of bar graphs,
but never seen bar graphs used to represent
continuous form of grouping.
Let's see how we can do that.
The first thing that we do is draw the 'x' and the 'y' axes.
We draw the axes and make equal intervals on each of them.
Then we label the axes.
Since we want to represent the quantity of each class interval,
we have the pens sold in the 'y' axis, and the price range of pens on the 'x' axis.
The steps are similar to the ones we use to draw a Bar graph.
Now we have to choose a suitable scale for the 'y' axis.
The number of pens sold range between 5 and 30.
A scale of 1 centimetre equals to 5 pens on the 'y' axis
would be perfect as we would need just 6 divisions.
We start writing the values on the 'y' axis.
5, 10, 15 and so on up to 30.
And on the 'x' axis, we start writing the price range of pens.
The first range is 10 to 20.
Then 20 to 30 and so on up to 50 to 60.
That's it! Now we just have to draw
appropriate bars for each class interval.
For the range 10 to 20, the frequency is 15.
So based on the scale we draw a Bar of length 3 centimetres.
For a frequency of 20, we draw a bar of length 4 centimeters.
And we continue the process till we reach the last range.
This is called a Histogram.
Bars used to represent continuous class intervals.
Remember, for Bar graphs we did not have intervals here.
We just had plain simple categories.
But here, we have intervals on one axis and quantity on the other.
What we did here was simple.
We choose a scale and draw bars for each continuous interval.
But note that the intervals were continuous.
20 which is the upper limit of the first interval,
is used as the lower limit for the next interval.
But what if the intervals are discontinuous?
We will understand that in another video.
