31 Jan 12. Assume that an event A contains 10

Exam: 250712RR – Probability

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Questions 1 to 20: Select the best answer to each question. Note that a question and its answers may be split across a page break, so be sure that you have seen the entire question and all the answers before choosing an answer.

1. For each car entering the drive-through of a fast-food restaurant, x = the number of occupants. In this study, x is a

A. continuous quantitative variable.

B. joint probability.

C. dependent event.

D. discrete random variable.

2. If the mean number of hours of television watched by teenagers per week is 12 with a standard deviation of 2 hours, what proportion of teenagers watch 16 to 18 hours of TV a week? (Assume a normal distribution.)

A. 4.2%

B. 2.1%

C. 4.5%

D. 0.3%

Protestant Catholic Jewish Other

Democrat 0.35 0.10 0.03 0.02

Republican 0.27 0.09 0.02 0.01

Independent 0.05 0.03 0.02 0.01

3. The table above gives the probabilities of combinations of religion and political parties in a city in the United States. What is the probability that a randomly selected person will be a Protestant and at the same time be a Democrat or a Republican?

A. 0.67

B. 0.62

C. 0.35

D. 0.89

4. A breeder records probabilities for two variables in a population of animals using the two-way table given here. Given that an animal is brown-haired, what is the probability that it’s short-haired?

Brown-haired Blond

Short-haired 0.06 0.23

Shaggy 0.51 0.20

A. 0.0306

B. 0.105

C. 0.222

D. 0.06

5. Tornadoes for January in Kansas average 3.2 per month. What is the probability that, next January, Kansas will experience exactly two tornadoes? A. 0.1304

B. 0.2226

C. 0.4076

D. 0.2087

6. A new car salesperson knows that she sells a car to one customer out of 20 who enter the showroom. Find the probability that she’ll sell a car to exactly two of the next three customers.

A. 0.1354

B. 0.0071

C. 0.0075

D. 0.9939

7. What is the value of ? A. 6720

B. 56

C. 1.6

D. 336

8. Approximately how much of the total area under the normal curve will be in the interval spanning 2 standard deviations on either side of the mean? A. 95.5%

B. 68.3%

C. 50%

D. 99.7%

9. The probability of an offender having a speeding ticket is 35%, having a parking ticket is 44%, having both is 12%. What is the probability of an offender having either a speeding ticket or a parking ticket or both? A. 67%

B. 55%

C. 91%

D. 79%

10. Each football game begins with a coin toss in the presence of the captains from the two opposing teams. (The winner of the toss has the choice of goals or of kicking or receiving the first kickoff.) A particular football team is scheduled to play 10 games this season. Let x = the number of coin tosses that the team captain wins during the season. Using the appropriate table in your textbook, solve for P(4 ≤ x ≤ 8).

A. 0.246

B. 0.171

C. 0.377

D. 0.817

11. If event A and event B are mutually exclusive, P(A or B) = A. P(A) + P(B) – P(A and B).

B. P(A) + P(B).

C. P(A) – P(B).

D. P(A + B).

12. Assume that an event A contains 10 observations and event B contains 15 observations. If the intersection of events A and B contains exactly 3 observations, how many observations are in the union of these two events? A. 0

B. 22

C. 28