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Unformatted text preview: Midterm 1 { Practice Problems Part 2 1. Let X denote the time, in minutes, it takes Alicia to drive to school. Suppose X has the distribution below. (a) What type (discrete of continuous) of random variable is X ? Explain. (b) What’s the minimum amount of time it takes Alicia to get to school? (c) What’s the probability that it takes Alicia more than 40 minutes to get to school? 2. You must pass an incredibly di cult exam in order to stay in school. You estimate the probability for the minimum required number of weeks of preparation necessary and thus create the following distribution: x 1 2 3 4 5 P X ( x ) 0.05 0.05 0.1 0.2 0.3 0.3 (a) Calculate the average number of weeks of preparation necessary. (b) Calculate the variance and standard deviation of X . Be sure to label which is which. (c) What is the probability that X di ers from its mean by at most 1 standard deviation? 3. A bookstore puts one probability book and two statistics books on the shelf. The probability book has a .6 chance to be sold, and if it is sold, the probabilities that none, one, or two of the statistics books are sold are .2, .5, and .3, respectively. If the probability book is not sold, the probabilities of selling none, one, or two statistics books become .4, .4, and .2, respectively. (a) Draw a probability tree summarizing the information. (b) Given that two books are sold, nd the probability that exactly one probability book and one statistics book are sold....
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 Fall '06
 Haskell

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