For an ideal average 1- rigidly defined 2- easy to understand and easy to calculate 3- based upon all the observation 4- suitable for further mathematical treatments. 5- should not be affected much by extreme values.

Arithmetic mean – sum of observation divided by number of observations n A.M for raw data x = 1/n ∑ xi i=1 A.M for grouped data x = 1/N ∑ fi xi i-1 A. M is the best measure of central tendency

H.M for raw data H.M. = ----------------- Harmonic mean - Reciprocal of the arithmetic average of the reciprocal of observation. 1 H.M for raw data H.M. = ----------------- 1 n -- ∑ (l/xi) n i – 1 N H.M for grouped data H.M = ----------------------- -- ∑ (fi/xi) N i - 1

Geometric mean (G.M) –the nth root of the products of all observations G.M for raw data G.M = antilog --- ∑ 1og xi n i=1 1 n G.M for grouped data = antilog --- ∑ fi log xi N i=1  

Median – value which divides the distribution into two equal parts n+1 Median for raw data. Median = (-------)th 2 the ascending order N/2-m2 Median for grouped data Median =l2+[-----------] f2

Mode - value which occur most frequently - peak value of the distribution Mode for raw data mode = repeated values Mode for grouped data (f-fp)c Mode = L+[----------------] 2f-fp-ts