Probability I: Introductory Ideas

The breakdown by political party of the 435 members of the U.S. House of Representatives before and after the 1992 Congressional elections was

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A produce shipper has 10,000 boxes of bananas from Ecuador and Honduras. An inspection has determined the following information:

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Marcia Lerner will graduate in 3 months with a master’s degree in business administration. Her school’s placement offi ce indicates that the probability of receiving a job offer as the result of any given on-campus interview is about 0.07 and is statistically independent from interview to interview. (a) What is the probability that Marcia will not get a job offer in any of her next three interviews? (b) If she has three interviews per month, what is the probability that she will have at least one job offer by the time she fi nishes school? (c) What is the probability that in her next fi ve interviews she will get job offers on the third and fi fth interviews only?

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A standard set of pool balls contains 15 balls numbered from 1 to 15. Pegleg Woodhull, the famous blind poolplayer, is playing a game of 8-ball, in which the 8-ball must be, the last one hit into a pocket. He is allowed to touch the balls to determine their positions before taking a shot, but he does not know their numbers. Every shot Woodhull takes is successful. (a) What is the probability that he hits the 8-ball into a pocket, on his fi rst shot, thus losing the game? (b) What is the probability that the 8-ball is one of the fi rst three balls he hits? (c) What is the probability that Pegleg wins the game, that is, that the 8-ball is the last ball hit into a pocket?

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BMT, Inc., is trying to decide which of two oil pumps to use in its new race car engine. One pump produces 75 pounds of pressure and the other 100. BMT knows the following probabilities associated with the pumps:

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Sandy Irick is the public relations director for a large pharmaceutical fi rm that has been attacked in the popular press for distributing an allegedly unsafe vaccine. The vaccine protects against a virulent contagious disease that has a 0.04 probability of killing an infected person. Twenty-five percent of the population has been vaccinated.

A researcher has told her the following: The probability of any unvaccinated individual acquiring the disease is 0.30. Once vaccinated, the probability of acquiring the disease through normal means is zero. However, 2 percent of vaccinated people will show symptoms of the disease, and 3 percent of that group will die from it. Of people who are vaccinated and show no symptoms from the vaccination, 0.05 percent will die. Irick must draw some conclusions from these data for a staff meeting in 1 hour and a news conference later in the day.

  1. If a person is vaccinated, what is the probability of dying from the vaccine? If he was not vaccinated, what is the probability of dying?
  2. What is the probability of a randomly selected person dying from either the vaccine or the normally contracted disease?

The pressroom supervisor for a daily newspaper is being pressured to find ways to print the paper closer to distribution time, thus giving the editorial staff more leeway for last-minute changes. She has the option of running the presses at “normal” speed or at 110 percent of normal—“fast” speed. She estimates that they will run at the higher speed 60 percent of the time. The roll of paper (the newsprint “web”) is twice as likely to tear at the higher speed, which would mean temporarily stopping the presses,

  1. If the web on a randomly selected printing run has a probability of 0.112 of tearing, what is the probability that the web will not tear at normal speed?
  2. If the probability of tearing on fast speed is 0.20, what is the probability that a randomly selected torn web occurred on normal speed?

Refer to Exercise 4-83. The supervisor has noted that the web tore during each of the last four runs and that the speed of the press was not changed during these four runs. If the probabilities of tearing at fast and slow speeds were 0.14 and 0.07, respectively, what is the revised probability that the press was operating at fast speed during the last four runs?

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Airlines serve as ''flagship carriers'' in Europe, and for symbolic and strategic reasons, many have been state owned. But governments have had to pay heavy subsidies and some airlines have been privatized. The competitive marketplace appears to reward this move.In 1994, of ten major airlines, five were privately owned and five were under state control.

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In the summer of 1995, Boeing successfully introduced into commercial airline service the 777, a large plane capable of carrying more than 300 passengers. They immediately sought approval from the Federal Aviation Authority for long, transoceanic flights such as the Denver to Honolulu route.

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