what are the characteristics of arithmetic mean ?
MEANING OF ARITHMATIC MEAN :
The arithmetic mean of a data set is defined to be the sum of all the observations of the data set divided by the total number of observations in the data set.
If be the values assumed by a variable then their arithmetic mean or A.M. is defined as:
PROPERTIES OF ARITHMATIC MEAN :

The sum of the deviations, of all the values of x, from their arithmetic mean, is zero.
Justification :
Since is a constant,
 The product of the arithmetic mean and the number of items gives the total of all items.
Justification :
or
 If and are the arithmetic mean of two samples of sizes n_{1} and n_{2}respectively then, the arithmetic mean of the distribution combining the two can be calculated as
This formula can be extended for still more groups or samples.
Justification : = total of the observations of the first sample
Similarly = total of the observations of the first sample
The combined mean of the two samples
=
=