Question

What is the class mark of the class $100 - 150$?
A) $100$
B) $125$
C) $130$
D) $150$

Answer 1

In this question we are given an interval and we have been asked the class mark. Class mark is nothing but the average of the upper limit and the lower limit. Just add the two limits and divide the sum by two. The resultant will be the answer.

Formula used: $\left( {\dfrac{{{\text{Upper limit + Lower limit}}}}{2}} \right)$

Complete step-by-step solution:
Before finding the class mark, let us know a little about what a class mark is? And what are its uses?
Class mark is the mid-point of a class-interval. We can say that the class mark is the mean of the upper limit and lower limit of the class. It can be calculated by adding the upper limit and lower limit and dividing the sum by 2.
Now, let us move towards the question.
We have upper limit = $150$,
Lower limit = $100$.
Step1: Would like to add them.
Upper limit + lower limit = $100 + 150 = 250$
Step2: To divide the sum by 2.
$\Rightarrow \dfrac{{250}}{2} = 125$

$\therefore$ Our answer is option B) 125.

Note: There are two terms between which students often get confused-

1. Class width- This refers to the difference between the upper limit and the lower limit. It is also known as class size. It remains the same for all the intervals.
2. Class mark- It is the average of the upper limit and the lower limit. It changes for every class interval.