At a manufacturing assembly, 30 jobs arrive per hour. Each job must pass through two production stage: stage1 and stage2. Stage1 takes an average of 1 minute to complete, and one worker is available to perform stage1. after completing stage1, the job immediately passes to stage 2. stage 2 takes an average of 2 minutes to complete, and two workers are available to work on stage2. after completing stage2, each job is inspected. Inspection takes 10% of the jobs must be returned to stage1 and they then repeat both stages1 and 2. after inspection 20% of all jobs return to stage2 and repeat stage2. Assume that inter-arrival times and service time are exponential.
What is the average time a job spends in the system from arrival to completion?
What percentage of the time during which each worker is busy?