Solution: Given = Arrival rate= 60/15= 4 = service rate= 60/10= 6 a. Percentage of time July idle is = 1- / = 1-4/6= 0.33= 33% b. A student spends the following amount of waiting time on an average can be calculated using the following formula: Lq= 2/ (- ) = 42 / 6(6-4) = 16/12 = 1.33 W q is the average waiting time and can be calculated using the following formula: Wq= Lq/ = 1.33/ 4 = 0.33 = 0.33*60 = 20 minutes on average c. Lq is the average number of students waiting and can be calculated using the following formula: Lq = 2/ (- ) = 42 / 6(6-4) = 16/12 = 1.33 Therefore, on average 1.33 students have to wait in line. d. The required probability is calculated using the following formula: Pn = (1- /) (/)n P0= (1-4/6) (4/6)0 = 0.3333 Similarly, P1= 0.2222 P2= 0.1481 P3= 0.0986 P = 1- (P0 P1 P2 P3) P= 1- (0.8017) P= 0.1983= 19.83% Answer Thus the probability of at least three students in the system is about 20%