Question : If the probability of a defective bolt is 0.1, find (i) the mean and (ii) the standard deviation for the distribution of defective bolts in a total of 400.

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Pr(X = def) = 0.1

Pr(Y = not def)= 1-0.1 = 0.9

$\displaystyle \mu = \sum x. Pr(X) $................I dont know what should i put in the value of x