NCERT Solutions
Class 11 Maths
Probability

Ex.15.1 Q.2
Find the mean deviation about the mean for the data
38, 70, 48, 40, 42, 55, 63, 46, 54, 44
The given data is
38, 70, 48, 40, 42, 55, 63, 46, 54, 44
Mean of the data, X = (38 + 70 + 48 + 40 + 42 + 55 + 63 + 46 + 54 + 44) ÷ 10 = 500 ÷ 10 = 50
The deviations of the respective observations from the mean X i.e., xi – X are
–12, 20, –2, –10, –8, 5, 13, –4, 4, –6
The absolute values of the deviations, i.e., |xi – X|, are
12, 20, 2, 10, 8, 5, 13, 4, 4, 6
The required mean deviation about the mean is
MD(X) = (Σi=110|xi – X|) ÷ 10 = (12 + 20 + 2 + 10 + 8 + 5 + 13 + 4 + 4 + 6) ÷ 10 = 84 ÷ 10 = 8.4