Question

Find the quartile deviation and coefficient of quartile deviation of the marks from the following frequency distribution of marks of 43 students of a school;

Marks	10	20	30	40	50	60
No. of students	4	7	15	8	7	2

Answer 1

First Quartile :

Q₁ = Value of \(\left(\frac{n+1}{4}\right)\)th observation

= Value of \(\left(\frac{43+1}{4}\right)=\frac{44}{4}\) = 11th observation

Referring to column cf,

Q₁ = 20 marks

Third Quartile :

Q₃ = Value of \(\left(\frac{n+1}{4}\right)\)th observation

= Value of 3(11)

= 33 rd observation Referring to column cf,

Q₃ = 40 marks

Quartile deviation of marks: