operations research2 questions

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An assembly line has three stations through which every unit being produced must pass in the same fixed order. The arrival of units follows a Poisson process for all stations. The mean time between arrivals is 8 minutes. The stations operate independently and queues are allowed to form in front of each station. All stations have same mean processing time of 4 minutes. If processing time at each station has an exponential distribution The average number of units in the assembly line is: a. Less than 1. b. Greater than or equal to I but less than 3. c. Greater than or equal to 3 but less than 5 d. Greater than or equal to 5 An assembly line has three stations through which every unit being produced must pass in the same fixed order. The arrival of units follows a Poisson process for all stations. The mean time between arrivals is 8 minutes. The stations operate independently, and queues are allowed to form in front of each station. All stations have same mean processing time of 4 minutes. If processing time at each station has an exponential distribution The total spent minutes in the assembly line for each unit is. a. less than 12. b. Greater than or equal to 12 but less than 24. c. Greater than or equal to 24 but less than 27 d. Greater than or equal to 27