Portland State University



Stat243BU Quiz #3A Spring 2015 Students can use a page of note (front and back) prepared by themselves and a calculator. However, class notes and textbooks are not allowed. Each problem is of 5 points worth. NAME: KEY1. A numerical description of the outcome of an experiment is called aa.descriptive statisticb.probability functionc.varianced.random variableANS:D2. A probability distribution showing the probability of x successes in n trials, where the probability of success does not change from trial to trial, is termed aa.uniform probability distributionb.binomial probability distributionc.hypergeometric probability distributiond.normal probability distributionANS:B3. Which of the following is a required condition for a discrete probability function?a.?f(x) = 0b.f(x) 1 for all values of xc.f(x) < 0d.?f(x) = 1ANS:D4. The number of electrical outages in a city varies from day to day. Assume that the number of electrical outages (X) in the city has the following probability distribution.xp(x)00.8010.1520.0430.01The mean and the standard deviation for the number of electrical outages (respectively) area.2.6 and 5.77b.0.26 and 0.577c.3 and 0.01d.0 and 0.8ANS:BProblems 5 – 8: The probability that Pete will catch fish when he goes fishing is .8. Pete is going to fish 3 days next week. Define the random variable X to be the number of days Pete catches fish.5.The probability that Pete will catch fish on exactly one day isa..008b..096c..104d..8ANS:B6.The probability that Pete will catch fish on one day or less isa..008b..096c..104d..8ANS:C7.The expected number of days Pete will catch fish isa..6b..8c.2.4d.3ANS:C 8. The variance of the number of days Pete will catch fish isa..16b..48c..8d.2.4ANS:B 9. Range rule of thumb for a usual observation is a..6 ± 2(.4)b..8 ± 2(.16)c.2.4 ± 2(.693)d.3 ± 2(.48)ANS:CProblems 10 – 11: The random variable X is the number of occurrences of an event over an interval of ten minutes. It can be assumed that the probability of an occurrence is the same in any two-time periods of an equal length. It is known that the mean number of occurrences in ten minutes is 5.3.10.The probability that there are 8 occurrences in ten minutes isa..0241b..0771c..1126d..9107ANS:B11.The probability that there are less than 3 occurrences isa..0659b..0948c..1016d..1239ANS:C ................
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