In: Electrical Engineering
A supermarket you work part-time at has one express lane open
from 5 to 6 PM on weekdays (Monday through Friday). This time of
the day is usually the busiest since people tend to stop on their
way home from work to buy groceries. The number of items allowed in
the express lane is limited to 10 so that the average time to
process an order is fairly constant at about 1 minute. The manager
of the supermarket notices that there is frequently a long line of
people waiting and hears customers grumbling about the wait. To
improve the situation he decides to open additional express lanes
during this time period. If he does, however, he will have to
"pull" workers from other jobs around the store to serve as
cashiers. Hence, he is reluctant to open more lanes than
necessary.
Knowing that you are a college student studying probability, your
manager asks you to help him decide how many express lanes to open.
His requirement is that there should be no more than one person
waiting in line 95% of the time.
With the task at hand, you set out to study the problem first. You
start by counting the number of customer arrival in the express
lane on a Monday from 5 to 6pm. There are a total of 81 arrivals.
You repeat the experiment on the following four days (Tuesday
through Friday) and note the total arrivals of 68, 72, 61 and 66
customers, respectively.
1) What is the average number of customer arrivals at the express
lane from 5 to 6pm on weekdays?
2) Assume the customer arrivals at the express lane from 5 to 6pm on weekdays can be modeled by a Poisson random variable, what is the PMF for the number of customers arrived during a one-minute interval in this period?
3) What is the probability of two or fewer customers arriving at the one express lane during a oneminute interval in this period? Does it satisfy the manager’s requirement of no more than one person waiting in line 95% of the time?
4) If your answer to the previous question is no, how many
express lanes should the manager open in order to satisfy his
requirement? You can assume that the arriving customer is equally
likely to join any of the express lane if there are more than one
express lanes. Also you can assume the lanes are independent, but
all lanes must satisfy the manager’s requirement.