In statistics, one type of average, also known as arithmetic mean (to differentiate it from geometric mean). In any numerical sample, the (arithmetic) mean is derived by dividing the sum by the number of members in the sample. Thus, in the series 2,3,4,5,5,5,7,8,9,9, the mean is 5.7, because the sum is 57 and there are 10 numbers in the sample ( 57 / 10 = 5.7 ).
(See also: mode, median)