Shortly after being put into service some buses manufactured

Shortly after being put into service, some buses manufactured by a certain company have developed cracks on the underside of the main frame. Suppose a particular city has 20 of these buses, and cracks have actually appeared in 8 of them. a) How many ways are there to select a sample of 5 buses from the 20 for a thorough inspection? b) In how many ways can a sample of 5 buses contain exactly 4 with visible cracks? c) If a sample of 5 buses is chosen at random, what is the probability that exactly 4 of the 5 will have visible cracks? d) If buses are selected as in part (c), what is the probability that at least 4 of those selected will have visible cracks?

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Solution

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http://www.stat.ucla.edu/~dinov/courses_students.dir/09/Spring/STAT35.dir/HWs.dir/HW3_sol.pdf