how to make a discrete class to a continuous class for e.g.--- 0-17 67-85
Consider the distribution
| xi | 10 – 14 | 15 – 19 | 20 – 24 | 25 – 29 | 30 – 34 |
| fi | 8 | 10 | 25 | 12 | 7 |
The given frequency distribution is not continuos.
Difference between the lower limit of a class and the upper limit of the preceding class is 1 i.e. h = 1. To convert the given frequency distribution into a continuos frequency distribution, subtract 
from each lower limit and add 
to each upper limit.
The continous distribution obtained is given as
| xi | 9.5 – 14.5 | 14.5 – 19.5 | 19.5 – 24.5 | 24.5 – 29.5 | 29.5 – 34.5 |
| fi | 8 | 10 | 25 | 12 | 7 |