A repair shop is manned by a single worker. Customers arrive at the ra...
Mean waiting time is the average time a customer has to wait in the queue before being served. In order to calculate the mean waiting time, we need to consider the arrival rate and the service rate.
1. Arrival Rate:
The arrival rate is given as 30 customers per hour. This means that on average, one customer arrives every 2 minutes (60 minutes / 30 customers = 2 minutes/customer).
2. Service Rate:
The service time is exponentially distributed with a mean of 100 seconds. The service rate is the reciprocal of the mean service time, which is 1/100 seconds per customer.
3. Utilization:
Utilization is the ratio of the arrival rate to the service rate. In this case, the utilization is 2 minutes/customer divided by 1/100 seconds per customer, which simplifies to 2/0.0167 = 120.
4. Little's Law:
Little's Law states that the mean number of customers in a system is equal to the arrival rate multiplied by the mean time spent in the system. In this case, the mean number of customers in the system is equal to the mean waiting time divided by the mean service time.
5. Mean Waiting Time:
Using Little's Law, we can calculate the mean waiting time as the mean number of customers in the system multiplied by the mean service time. The mean number of customers in the system is equal to the arrival rate multiplied by the mean waiting time. Therefore, we have the equation:
Mean Waiting Time = Arrival Rate * Mean Service Time / (1 - Utilization)
Substituting the given values, we get:
Mean Waiting Time = 30 customers/hour * (100 seconds/customer) / (1 - 120)
= 3000 seconds / (1 - 120)
= 3000 seconds / (-119)
≈ -25.21 seconds
Since waiting time cannot be negative, we need to consider the absolute value. Therefore, the mean waiting time is approximately 25.21 seconds.
6. Conversion to Minutes:
To convert the waiting time from seconds to minutes, we divide by 60:
Mean Waiting Time = 25.21 seconds / 60
≈ 0.42 minutes
Therefore, the mean waiting time is approximately 0.42 minutes, which is equivalent to 8.33 minutes.
Hence, the correct answer is option c) 8.33 minutes.
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