If the probability of a defective bolt is 0.1, find the (i) mean and (ii) standard deviation for the distribution of bolts in a total of 400 bolts.
Let p = probability of selecting defective bolt, so
p = 0.1
q = 1 – p
Given, n = 400,
(i) mean = np
(ii) Standard deviation = 
= 
= 
∴ Standard deviation = 6
So, mean = 40, standard deviation = 6
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