Question

The class marks of intervals $20-30$ and $10-20$ are:

• A. $25$ and $10$
• B. $25$ and $15$
• C. $20.5$ and $10.5$
• D. $20.5$ and $30.5$

Answer 1

The correct option is B $25$ and $15$

Class mark is the average of upper limit and lower limit of the given class interval.

Therefore, class mark of $20-30$ interval is $\frac{20+30}{2}=\frac{50}{2}=25$

Class mark of $10-20$ interval is $\frac{10+20}{2}=\frac{30}{2}=15$