Page 1 - Lesson Note MCT 2 55

SAI INTERNATIONAL SCHOOL

ECONOMICS

Class-XI

CHAPTER 9

Measures of Central Tendency – Quartiles.

(Lesson Note - 55)

TOPICS TO BE COVERED-

- calculate quartiles in case of individual series.

- calculate quartiles in case of discrete series.

-calculate quartiles in case of continuous series.

Quartiles: -

Just like median, quartiles divide the series into four equal parts such
that each part comprises of 25% of the data in the series. There are all
total 3 quartiles such as , and .
3
2
1
25% of data≤ ≤ 75% of data.
1
50% of data≤ ≤ 50% of data.
2
75% of data≤ ≤ 25% of data.
3
=
2

Steps to calculate Quartiles in case of Individua series: -

 First arrange the data either in ascending or descending order.
+1
 Lower quartile ( ) = Size of ( )th item. Where, n: - no of data.
1
4
3( +1)
 Upper quartile ( ) = Size of ( 4 )th item. Where, n: - no of data.
3

Ex: Marks of five students are 42, 40, 60, 55, 65, 35 and 50 calculate lower
quartile and upper quartile.