Question

the fourth class interval for a grouped data whose first and second class intervals are 10 - 15 and 15 - 20 respectively is

Explanation:

Step1: Identify class - width

The class - width is found by subtracting the lower limit of the second class from the lower limit of the first class. For the classes 10 - 15 and 15 - 20, the class - width $w=15 - 10=5$.

Step2: Find the third class interval

The third class interval will start where the second class interval ends. Since the second class is 15 - 20, the third class interval is 20 - 25 (because the lower limit of the third class is 20 and the class - width is 5).

Step3: Find the fourth class interval

The fourth class interval will start where the third class interval ends. Since the third class is 20 - 25, the fourth class interval is 25 - 30 (because the lower limit of the fourth class is 25 and the class - width is 5).

Answer:

25 - 30