Question

in the class intervals 10 - 20, 20 - 30, etc., the class that includes 20 is

Explanation:

Step1: Understand class - interval convention

In exclusive - type class intervals, the upper - limit of one class is the lower - limit of the next class. The value equal to the upper - limit of a class is included in the next class.

Step2: Identify the class for 20

Since 20 is the upper - limit of the class interval 10 - 20 and the lower - limit of the class interval 20 - 30, 20 is included in the class interval 20 - 30.

Answer:

20 - 30