The following table presents the probability distribution of the number of vacations X taken last year for a randomly chosen family. Compute the standard deviation .
x 0 1 2 3 4
p(x) .07 .66 .16 .07 .04
Solution :
Mean = = X * P(X)
= 0 *0.07 + 1 * 0.66+ 2 *0.16 + 3 *0.07 + 4 *0.04
= ( 0+ 0.66 + 0.32 +0.21+0.16 )
= 1.35
Standard deviation =
=X 2 * P(X) - 2
= [ 02 * 0.07 + 12 * 0.66+ 22 *0.16 + 32 *0.07 + 42 *0.04] -1.352
= [( 0+ 0.66+0.64 +0.63+0.64 ) )] -`1.8225
= 2.57 -1.8225
=0.7475
=0.8646
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