The following probability mass function is for a random variable of the number of customers serviced by a bank teller:

Assuming the mid value of the range to represent the x value for the probability mass function,

(a) compute the expected value of X,

(b) compute the variance and standard deviation,

(c) compute the probability that X ≥ 301.

x (rang) Px(x) [0,100] 0.10 [101,200] 0.20 [201,300] 0.30 [301,400] 0.2 [401,500] 0.2