STAT 500 – Applied StatisticsDepartment of Statistics

Practice Exam

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Problem 1. [18 pts (4+4+6+4)]

An airline claims that the proportion of its flights being on time is more than 0.75. We take a random sample of 7 flights.

a. What is the expected value of the number of flights that arrive on time, if the proportion of on time flights is indeed 0.75? If it is not a whole number, should you round it to a whole number for the expected value?

b. What is the standard deviation of the number of on-time flights, if the proportion of on time flights is indeed 0.75?

c. What is the probability of at least 2 (i.e., two or more) out of the 7 flights being on time, if the proportion of on-time flights is in-deed 0.75?

d. Choose the correct answer: the value 2/7 given in part c of this problem is:

i. A statistic

ii. A parameter

iii. Sample size