A mail-order computer business has six telephone lines. Let x denote the number of lines in use at a specified time. Suppose the mass function of x is given by x: 0 1 2 3 4 5 6 p(x): 0.1 0.15 0.20 0.25 0.20 0.05 ? a) What is the missing probability when x = 6 telephone lines. b) Calculate the value of the mean of x. c) Calculate the value of the standard deviation of x. d) What proportion of this computer business will have at least 3 telephone lines in use? e) What proportion of this computer business will have at most 5 telephone lines in use? f) For what proportion of this computer business will the number of telephone lines in use be within 1 standard deviation of the mean value?