(b) Class intervals
Ans. The difference between the Upper and Lower limits of a class is known as class interval of that class. For example, in the class (10-20), the class interval is 10 (i.e., 20 minus 10).

(c) Types of class intervals
Ans. Following are the types of class intervals:
(i) Where both the class limits are specifically stated either in an "inclusive manner or in an exclusive manner". For example,

Inclusive Manner			Exclusive Manner
10-14 15-19 20-24		Both values included	10-15 15-20 20-25		Upper values excluded

(ii) The intervals may be represented by mid-points of the class intervals. For example,