Question

1. The U.S. Department of Transportation reported that during November, 83.4% of Southwest
Airlines’ flights, 75.1% of US Airways’ flights, and 70.1% of JetBlue’s flights arrived on time (USA
Today, January 4, 2007). Assume that this on-time performance is applicable for flights arriving at
concourse A of the Rochester International Airport, and that 40% of the arrivals at concourse Aare
Southwest Airlines flights, 35% are US Airways flights, and 25% are JetBlue flights.
a. An announcement has just been made that Flight 1424 will be arriving at gate in concourse A.
What is the most likely airline for this arrival?
c. What is the probability that Flight 1424 will arrive on time?
d. Suppose that an announcement is made saying that Flight 1424 will be arriving late. What is the
most likely airline for this arrival? What is the least likely airline?

2. In San Francisco, 30% of workers take public transportation daily (USA Today, December 21, 2005).
a. In a sample of 10 workers, what is the probability that exactly three workers take public
transportation daily?
b. In a sample of 10 workers, what is the probability that at least three workers take public
transportation daily?

3. Auniversity found that 20% of its students withdraw without completing the introductory statistics
course. Assume that 20 students registered for the course.
a. Compute the probability that two or fewer will withdraw.
b. Compute the probability that exactly four will withdraw.
c. Compute the probability that more than three will withdraw.
d. Compute the expected number of withdrawals.

4. Phone calls arrive at the rate of 48 per hour at the reservation desk for Regional Airways.
a. Compute the probability of receiving three calls in a 5-minute interval of time.
b. Compute the probability of receiving exactly 10 calls in 15 minutes

.
5. More than 50 million guests stay at bed and breakfasts (B&Bs) each year. The website for the Bed
and Breakfast Inns of North America, which averages seven visitors per minute, enables many
B&Bs to attract guests (Time, September 2001).
a. Compute the probability of no website visitors in a one-minute period.
b. Compute the probability of two or more website visitors in a one-minute period.

6. In a survey conducted by the Gallup Organization, respondents were asked, “What is your favorite
sport to watch?” Football and basketball ranked number one and two in terms of preference
(Gallup website, January 3, 2004). Assume that in a group of 10 individuals, seven prefer football
and three prefer basketball. A random sample of three of these individuals is selected.
a. What is the probability that exactly two prefer football?
b. What is the probability that the majority (either two or three) prefer football?

Answer 1