答案和详解如下： 1、A random variable X is continuous and bounded between zero and five, X 0≤X≤5). The cumulative distribution function (cdf) for X is F(x)=x/5. Calculate P(2≤X≤4). A) 1.00. B) 0.25. C) 0.40. D) 0.50. The correct answer was C) For a continuous distribution, P(a≤X≤b) = F(b)-F(a). Here, F(4) = 0.8 and F(2) = 0.4. Note also that this is a uniform distribution over 0≤x≤5 so Prob(2<x<4) = (4-2)/5 = 40% 2、Which of the following qualifies as a cumulative distribution function? A) F(1)=0.5, F(2)=0.25, F(3)=0.25. B) F(1)=0, F(2)=0.5, F(3)=0.5, F(4)=0. C) F(1)=0.3, F(2)=0.6, F(3)=0.3. D) F(1)=0, F(2)=0.25, F(3)=0.50, F(4)=1. The correct answer was D) Because a cumulative probability function defines the probability that a random variable takes a value equal to or less than a given number, for successively larger numbers, the cumulative probability values must stay the same or increase. | 
发表于 2008-4-10 14:07
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