| Class Mark | $6$ | $12$ | $18$ | $24$ | $30$ | $36$ |
| Frequency | $8$ | $12$ | $15$ | $18$ | $25$ | $7$ |
Solution:-
Steps to draw histograms for given frequency distributions,
1. First we have to calculate the class interval from the class mark using the following adjustment formula.
Value of Adjustment = (One class mark $–$ Preceding class mark)/$2$
Then, the value obtained is added to the class mark to obtain the upper limit and subtracted from the class mark to obtain lower limit.
Now,
Value of adjustment $=(12–6)/2$
$=6/2$
$=3$
So, we add and subtract $3$ to each class mark to obtain the class interval.
The lower limit of first class $=6–3=3$
The Upper limit of first class $=6+3=9$
Hence, the first class interval is $(3–9)$.
Similarly, we can calculate the remaining class intervals.
| Class Mark | $3–9$ | $9-15$ | $15–21$ | $21–27$ | $27–33$ | $33–39$ |
| Frequency | $8$ | $12$ | $15$ | $18$ | $25$ | $7$ |
2. On the x – axis, take $1cm=10$ units and plot frequency.
3. On the y – axis, take $1cm=10$ units and plot class interval.
4.Construct rectangles of histograms according to given data.