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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