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A certain course has a freshmen, b sophomores, c juniors, and d seniors. Let X be the
Chapter 7, Problem 66(choose chapter or problem)
A certain course has a freshmen, b sophomores, c juniors, and d seniors. Let X be the number of freshmen and sophomores (total), Y be the number of juniors, and Z be the number of seniors in a random sample of size n, where for Part (a) the sampling is with replacement and for Part (b) the sampling is without replacement (for both parts, at each stage the allowed choices have equal probabilities). (a) Find the joint PMF of X, Y, Z, for sampling with replacement. (b) Find the joint PMF of X, Y, Z, for sampling without replacement.
Questions & Answers
QUESTION:
A certain course has a freshmen, b sophomores, c juniors, and d seniors. Let X be the number of freshmen and sophomores (total), Y be the number of juniors, and Z be the number of seniors in a random sample of size n, where for Part (a) the sampling is with replacement and for Part (b) the sampling is without replacement (for both parts, at each stage the allowed choices have equal probabilities). (a) Find the joint PMF of X, Y, Z, for sampling with replacement. (b) Find the joint PMF of X, Y, Z, for sampling without replacement.
ANSWER:Step 1 of 2
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If the students are selected with replacement, then the marginal and conditional distributions will be multinomial. Therefore, we have
Thus, the joint PMF of for sampling with replacement is:
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