$3.$ A Pizza store has $4$ operators that take calls from customers. Each call lasts $5$ minutes, on

average, with a standard deviation of $5$ minutes. A call arrives, on average, every $3$ minutes,

with a standard deviation of $3$ minutes. On average, how many minutes does a customer wait

before talking to an operator? You must use only the formula below when you find the answer.

$(15$ Points$)$

$=$

$2(+1)1$

$12$

$+2$

$$

$2$

$4.$ The organizers of a conference in the Houston Convention Center are evaluating the

possibility of setting up a computer area where attendees can check their e$-$mail on computers

provided by the organization. There will be one common queue for all computers and only one

person uses a computer at a time. On average, there are $15$ attendee arrivals per hour and the

average time a person spends on the computer is $10$ minutes. Organizers want to make sure

that the computer utilization rate is about $90\%$ so that the waiting time is not too long. At least

how many computers do they need to have? You must use only the formula below when you

find the answer. $(15$ Points$)$

$=$

$$