Question

The class marks of a frequency distribution are 15, 20, 25, 30, .. . The class corresponding to the class marks 20 is
(a) 12.5−17.5
(b) 17.5−22.5
(c) 18.5−21.5
(d) 19.5−20.5

Answer 1

(b) 17.5$-$22.5

We are given frequency distribution 15, 20, 25, 30,...
Class size = 20 $-$ 15 = 5
Class marks = 20
Now,
$$\begin{gathered} \mathrm{Lower}\mathrm{limit}=\left(20-\frac{5}{2}\right)=\frac{35}{2}=17.5 \\ \mathrm{Upper}\mathrm{limit}=\left(20+\frac{5}{2}\right)=\frac{45}{2}=22.5 \end{gathered}$$

Thus, the required class is 17.5$-$22.5.