Using the data of Exercise 129, show that the class marks also are given by the midpoint between successive class boundaries
(a) Construct a histogram of the drying times of polyurethane from the data in Exercise 115.
(b) What can be said about the shape of this histogram?
Exercise 115
The following are the drying times (minutes) of 100 sheets coated with polyurethane under various ambient conditions:
![](https://test.transtutors.com/qimg/98537660-8a89-44b6-a6fa-5d179a822250.png)
Construct a frequency distribution of these data, using eight classes.