Interpreting the mean variance of a probability distributions

*The number of cellular phones sold out per day at the E-Cell Retail Store with the corresponding probabilities is shown in the table below.Complete the mean, variance and standard deviation and interpret the result. Number of cellphones sold 15 18 19 20 22 per day in a retail store (x ) Probability(Px) 0.30 0.20 0.20 015 0.15 Solution: Complete the statement: Px=[{x/-P(x)]=15(0.30)+18(0.20)+19(0.20)+20(0.15)+22(0.15)= The mean is equal to therefore,it means that the average number of cellular phones of sold per day is ___. To find the variance complete the table below: X P(x) x-P(x) x2 x2.P(x) 15 0.30 4.5 18 0.20 3.6 19 0.20 3.8 20 0.15 3 22 0.15 3.3 [(x2.P(x)]= 02 = [(x2.P(x )-42= o=VO2= Therefore, the variance of probability distribution is equal to ,while the standard deviation is equal to