Question

Marks of the 100 students are distributed in the grouped frequency distribution table.

Class marks (Marks)	150	160	170	180	190	200
No. of Students	23	14	16	11	21	15

What is the class interval for the group having frequency 11 ?

• A. 170-180
• B. 175-185
• C. 160 - 170
• D. 165 - 175

Answer 1

The correct option is B 175-185

As class marks or midpoints are given, class intervals need to be calculated from the class marks.

Difference between the two successive classes = h = 160 - 150 =10.

If x is the class marks then, lower and upper boundary of every class is x - $\frac{h}{2}$ and x + $\frac{h}{2}$

Hence, for the group having frequency 11,

Lower boundary = 180 - $\frac{10}{2}$ = 175
Upper boundary = 180 + $\frac{10}{2}$ = 185

The class interval is 175 - 185.