Suppose mean of a series of 5 items is 30. Four values are respectively 10, 15,30 and 35. Estimate the missing 5th value of the series.
Suppose missing 5th item is 5 X.
__
Hence, X = 10+15+30+35+5X
5
= 90 + X
5
90 + X = 150
N = 150-90 = 60
Hence, missing value is 60.