Howell 9e_TBChapter 7

Chapter 7—Basic Concepts of Probability MULTIPLE CHOICE QUESTIONS 7.1 Which of the following is NOT an appropriate use of probability? a) estimating the likelihood that a particular event will occur b) calculating your chances of winning the lottery c) placing bets at the track d) *knowing what event will happen next 7.2 + Where is “subjective probability” most likely to be invoked? a) in setting the point spread in football b) *in deciding if tomorrow will be a good day c) in calculating your best strategy in poker d) in playing Russian roulette 7.3 + A frequentistic approach to probability is likely to be invoked a) in predicting the weather. b) in calculating the chances of winning in craps. c) *in estimating the probability that a sharpshooter will score a bull’s eye. d) in blackjack. 7.4 Which of the following is NOT a way of setting probabilities? a) the analytic view b) the frequentistic view c) the subjective view d) *the correlational view 7.5 Of 50 women treated for breast cancer in the local cancer unit, 35 of them survived for at least 5 years. For a woman who has just been diagnosed with breast cancer, our best guess is that the probability that she will survive for 5 years is a) *35/50 = .70 b) 15/35= .43 c) 35/100 = .35 d) we don’t have enough information. 7.6 + Out of a pool of 40 men and 10 women, all of whom are equally qualified for one position as an instructor in chemistry, the person hired was a male. The probability that this would happen if the department ignored gender as a variable in selection is a) .40 b) *.80 c) .50 d) .63

Test Bank 7.7 Last year there were 300 new Ph.D.s in chemistry looking for academic jobs. Of those, 100 were women and 200 were men. Nationwide last year there were 75 new hirings in chemistry departments. How many of those new hires would be expected to be women if there was no gender discrimination? a) 15 b) 20 c) *25 d) 50 7.8 Following up on the preceding question, suppose that you found that 27 of the new hires were women. You would probably be justified in concluding that a) there was discrimination against men. b) there was discrimination against women. c) *there was no discrimination on the basis of gender. d) we don’t have enough information to even start to answer the question. 7.9 + I am looking down on a parking lot, and can see that about 10% of the cars are red and about 15% of the cars are blue. To estimate the probability that the next car to leave the lot will be red or blue, I would a) *add those two percentages. b) multiply those two percentages. c) count the number of green cars. d) It can’t be estimated from the information provided. 7.10 In the parking lot below me, 40% of the vehicles are silver, and about 25% of the vehicles are pickup trucks. The probability that the next vehicle to leave the parking lot will be a silver pickup is a) .40 b) .65 c) .10 d) *It can’t be estimated without knowing that color and type of vehicle are independent. 7.11 To estimate that probability that the next vehicle to leave the parking lot will be a silver pickup, we first need to a) assume that the color and the type of vehicle are mutually exclusive. b) *assume that the color and the type of vehicle are independent. c) assume that the color and the type of vehicle are exhaustive. d) simply multiply the two probabilities. 7.12 + Two events are mutually exclusive when a) the occurrence of one event is independent of the occurrence of the other. b) *the occurrence of one event precludes the occurrence of the other. c) both events are equally likely. d) the first event precedes the second event. 251

Test Bank 7.18 One difference between the additive and the multiplicative rules that helps us remember when to use which is a) with the additive rule we are talking about the occurrence of one of several outcomes. b) with the multiplicative rule we are talking about the occurrence of more than one kind of outcome. c) the two rules are interchangeable. d) *both a and b 7.19 + If I am interested in the probability that you will be depressed and that you will have experienced a great deal of stress in the past month, I am talking about a) independence. b) *a joint probability. c) a conditional probability. d) an additive probability. 7.20 If I am interested in the probability that you will be depressed if you have experienced a great deal of stress in the past month, I am talking about a) independence. b) a joint probability. c) *a conditional probability. d) an additive probability. 7.21 When we are talking about joint probabilities we are likely to invoke a) *the multiplicative rule. b) the additive rule. c) the subjective probability rule. d) the law of joint probabilities. 7.22 The vertical bar “|” is read as _______ when we are talking about probabilities. a) “absolute” b) “not” c) “divide” d) *“given” 7.23 + I would like to calculate the probability that you will do well in this course if you are a member of a group of students who study together. The most important word in that last sentence is a) *“if.” b) “calculate.” c) “I.” d) “study.” 253

Chapter 7 7.24 Two events are said to be independent if a) the occurrence of one precludes the occurrence of the other. b) the occurrence of both is impossible. c) both events happen simultaneously. d) *the occurrence of one has no effect on the probability of the occurrence of the other. 7.25 A discrete variable is one that a) is kept a secret. b) we cannot estimate. c) *can take on a limited number of possible values. d) can take on any value between -  and +  . 7.26 A continuous variable is one that a) *can take on any value between two specified limits. b) we cannot estimate. c) can take on a limited number of possible values. d) can take on any value between -  and +  . 7.27 + Which of the following is most likely to be a discrete variable? a) the temperature outside your window b) *the number of courses you will take in college c) the length of time you can hold your breath d) the speed with which you can perform a task 7.28 For which kind of variable is the ordinate of a graph labeled as “density?” a) a discrete variable b) a positively skewed variable c) *a continuous variable d) an independent variable 7.29 + With continuous variables we a) cannot estimate probabilities because they are undefined. b) *need to speak about the probability of falling within a defined interval. c) can only speak about probabilities as subjective probabilities. d) can only calculate probabilities in whole units. 7.30 When we sample with replacement we a) only use subjects who have been selected on two separate occasions. b) *put the outcome back in the pool before sampling again. c) hold all outcomes out of the pool once they have been drawn. d) have probabilities that change after each draw. 254

Chapter 7 7.38 p(getting a job | knowing the manager) is the notation for the probability of a) getting a job or knowing the manager. b) getting a job and knowing the manager. c) *getting a job given that you know the manager. d) getting a job and not knowing what to give the manager. 7.39 We might find that 65% of women report themselves to be politically liberal, while only 52% of men report that they are liberal. The proportions would be described as a) erroneous. b) biased. c) *conditional on gender. d) independent. 7.40 When two teams compete against each other, the result for Team A can be win, draw, or lose. These events are a) independent. b) *exhaustive. c) joint. d) conditional. 7.41 Two events are mutually exclusive if a) *they cannot both happen at the same time. b) they cover all possibilities. c) one of them must happen. d) none of the above TRUE/FALSE QUESTIONS 7.42 [TRUE] The probability of rolling a 6 on the first roll with a standard die is independent of the probability of rolling a 6 on the second roll. 7.43 [TRUE] A bag of 100 hard candies included 30 butterscotch, 40 peppermint, 15 strawberry, 10 orange, and 5 banana. The probability that the first candy pulled out of the bag will be butterscotch or strawberry is .45. 7.44 [FALSE] The probability of getting heads twice when flipping a coin 2 times is .50. 7.45 [TRUE] When observing a continuous variable, you can calculate the probability that an event falls in a certain interval; and when observing a discrete variable, you can calculate the probability of a specific outcome. 7.46 [FALSE] Dealing 5 cards from a standard deck is an example of sampling with replacement. 7.47 [TRUE] Predicting the political party of the next president based on previous election patterns is an example of the relative frequency view of probability. 256

Test Bank 7.48 [TRUE] I have a hunch that tomorrow is going to be a bad day. This is an example of the subjective probability. 7.49 [FALSE] If the probability is .90 that a student taking this class is a Psychology major, and the probability that a student in this class has red hair is .05, then the joint probability of being a Psychology major and a red head in this class is .95. 7.50 [FALSE] The probability that a student is a Psychology major given that she is female is an example of joint probability. 7.51 [FALSE] The probability that an event will occur ranges from –1 to 1. OPEN-ENDED QUESTIONS 7.52 Identify each of the following examples as the analytic, relative frequency, or subjective view of probability based on the example of a brother and sister playing scrabble: a) If the brother and sister are equally matched, there is a .50 probability that each will win the game. b) If the sister won 3 of the last 4 games, the probability that she will win this one is .75. c) The brother believes there is an 80% chance that he will beat his sister this time. 7.53 Explain why it is important to know if someone is sampling with or without replacement when calculating the probability of multiple events. 7.54 Your friend plays the lottery every day. Since he has never won, he is convinced that the odds that he will win next time are even better. From a probability perspective, what is wrong with your friend’s logic? 7.55 A bag of 100 marbles contains 30 blue marbles, 25 green marbles, 25 mixed green/blue marbles, and 20 clear marbles. Marbles are returned to the bag after every draw. a) What is the probability of selecting a blue marble? b) What is the probability of selecting a blue or green marble? c) What is the probability of selecting a marble that is not clear? d) What is the probability of selecting a blue marble on the first draw and then a clear marble on the second draw? 7.56 Imagine the same bag of marbles, but this time, marbles are NOT returned to the bag after each draw. a) What is the probability of drawing 3 clear marbles in 3 draws? b) What is the probability of drawing a clear marble, then a green, and then a clear? c) What is the probability of not selecting any clear marbles in three draws? 257

Test Bank 7.61 A professor rated how frequently students actively participated in class and then calculated the probability of getting various grades broken down by participation. The data follow: A B C D F Frequently .06 .20 .03 .01 .00 Sometimes .03 .12 .20 .03 .02 Rarely/Never .01 .08 .07 .06 .08 a) What is the simple probability of getting an A? b) What is the probability of getting an A given the student participated frequently? c) What is the simple probability of failing? d) What is the probability of failing given the student participated rarely/never? 259