Question

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.

Answer 1

Total number of bolts (n) = 400 and p = prob of defective bolts = 0.1
(i) Mean = np = 400(0.1) =40

(ii) Variance = npq = 40(1-0.1) = 36

So, the standard deviation =\[\sqrt{36} = 6\]