Midwest Publishing publishes textbooks. The company uses an 800 number where people can call to ask questions about the textbooks and place orders. Currently, there are 2 representatives handling inquiries. Calls occurring when both lines are in use get a busy signal. Each representative can handle 12 calls per hour. The arrival rate is 20 calls per hour. Required:
a. How many extension lines should be used if the company wants to handle 90% of the calls immediately?
b. What is the probability that a call will receive a busy signal if your recommendation in part (a) is used?
c. What percentage of calls receive a busy signal for the current telephone system with two extension lines?

A. 18 calls

B. 0.9

C. 20

Step-by-step explanation:

Number of representatives=2,

Number of extension lines=2,

Average calls each representative can accommodate per hour = 15 calls,

Arrival rate per hour = 30 calls

(a) 90% of the arrival rate = 0.09 × 20 = 18 calls

To handle 18 calls immediately, 18 extension lines should be used

(b) Probability is given by number of possible outcomes ÷ number of total outcomes

Number of possible outcomes = 18, number of total outcomes = 20

Probability (call will receive busy signal) = 18/20 = 0.9

(c) For one extension line, numbers of calls to receive busy signal = 20 - 10 = 10 calls

Number of calls to receive busy signal for the current telephone system with two extension lines = 2 × 10 = 20 calls

the first one is x^2+2x+2

the second one is x^2+4

the last one is x^2-4x+8