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The second quartile also called median, and denoted by Qe, has 50% of the items, below it and 50% of the items above it., The third quartile, denoted by Qs, is the, median of the upper half of the data set., This means that about 75% of the numbers, in the data set lie below Q3 and about 25%, lie above Q3., , Deciles distribute the series into ten equal, parts and generally expressed as D., Percentiles divide the series into hundred, equal parts and generally expressed as P., Mode is the value which occurs most, frequently in the series, that modal value, has the highest frequency in the series., Main purposes and functions of averages., (i) To represent a brief picture of data., , (ii) Comparison., , (iii) Formulation of policies., , (iv) Basis of statistical analysis., , (v) One value for all the group or series., Essentials of a good average., , (i) Easy to understand., , (ii) Easy to compute, , (iii) Rigidly defined., , (iv) Based on all the items of series., , (v) Certain in character, , (vi) Least effect of a change in the sample.