Page 1 - Lession note - stat chap -9,MCT (AM)-47

Class-XI

STATISICS

CHAPTER-Measures of Central Tendency

Topic –Arithmetic Mean (Module-47)

Individual series

Short note

Measures of Central Tendency

Central Tendency
A central tendency refers to a central value or a representative value of
a statistical series.
According to Clark, “An average is a figure that represents the whole
group”.

Types of Statistical Averages
Averages are broadly classified into two categories

 Mathematical Averages
 Positional Averages

Arithmetic Mean
Arithmetic Mean is the number which is obtained by adding the values of
all the items of a series and dividing the total by the number of items.

Can be calculated under three heads -

 Direct Method According to this method, we find the Arithmetic mean from the
following formula

, , = Arithmetic Mean, Ex = Sum of all
values /items

 Short-cut Method By short cut method, we find the Arithmetic Mean from the
following formula

Here, = Arithmetic Mean, A = Assumed average , Ed = Net sum of the
deviations of the different values from the assumed average; and N = Number
of items in the series,

1
1
 Step deviation method , = A+ sum of d /N*c ,where d = d/c ,