Question

is the sixth class interval if the first two class intervals of a grouped data are 10 - 15 and 15 - 20?

Explanation:

Step1: Identify class width

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

Step2: Find the lower - limit of the sixth class

The lower - limit of the first class is $l_1 = 10$. The formula to find the lower - limit of the $n$th class is $l_n=l_1+(n - 1)w$. Here, $n = 6$, $l_1=10$ and $w = 5$. So, $l_6=10+(6 - 1)\times5=10 + 25=35$.

Step3: Determine the sixth class interval

Since the class width is 5, the sixth class interval is $35 - 40$.

Answer:

$35 - 40$