Find out the quartile deviation and coefficient of quartile deviation of the following series:

Explanation

`Q_(1)="Size of "((N+1)/(4))"th item"`
`="Size of "((11+1)/(4))"th item"`
`="Size of "` 3rd item
=20 marks
`Q_(3)="Size of " 3((N+1)/(4))"th item "`
`="Size of "((11+1)/(4))"th item"`
=Size of 9th item
=50 marks
Quartile Deviation (QD) `=(Q_(3)-Q_(1))/(2)=(50-20)/(2)=15`
Coefficient of Quartile Deviation `=(Q_(3)-Q_(1))/(Q_(3)+Q_(1))=(50-20)/(50+20)=(30)/(70)`
QD=15, Coefficient of QD=0.13
Note: `(Q_(3)-Q_(1))//2` or quartile deviation is average of the difference between two quartiles `(Q_(3)` and `Q_(1)`).