On the average 25 of the products manufactured by a certain

On the average, 25% of the products manufactured by a certain company are found to be defective. If we select four of these products at random and denote the number of the four products that arc defective by the random variable X, determine the mean and variance of X.

Solution

Mean ( np ) = 4 * 0.25 = 1
Standard Deviation ( npq )= 4*0.25*0.75 = 0.866
Variance = npq = 4*0.25*0.75 = 0.75