Question

What is the class mark of the class 135−155?

Answer 1

Hint: From the given class interval, we will find the lower class limit and the upper class limit which will be 135 and 155 respectively. Then, we have to substitute these values in the formula for class mark which is given by $\text{Class mark}=\dfrac{\text{Upper class limit}+\text{Lower class limit}}{2}$ .

Complete step by step answer:
We have to find the class mark of the class 135−155. We are given the class interval 135−155. Here, we can see that the lower class limit is 135 and the upper class limit is 155. We know that class mark is obtained by dividing the result of the sum of upper class limit and lower class limit by 2.
$\Rightarrow \text{Class mark}=\dfrac{\text{Upper class limit}+\text{Lower class limit}}{2}$
Let us substitute the values in the above formula.
$\Rightarrow \text{Class mark}=\dfrac{155+135}{2}$
We have to add the 155 and 135. We can write the result of this operation as
$\Rightarrow \text{Class mark}=\dfrac{290}{2}$
We have to divide 290 by 2.
$\Rightarrow \text{Class mark}=145$
Hence, the class mark of the class 135−155 is 145.

Note: Students may get confused with class mark and class size. Class mark is defined as the mid-value of each class interval is called its class mark. Class size is defined as the difference between the true upper limit and true lower limit of a class interval. We can write the formula for class size as
$\text{Class size}=\text{Upper class limit}-\text{Lower class limit}$
Students may get confused with the formula for class mark and write the same as
$\text{Class mark}=\dfrac{\text{Upper class limit}-\text{Lower class limit}}{2}$ which will lead to wrong answers.