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Math Forum » Discussions » sci.math.* » sci.stat.math.independent

Topic: Probability of selecting {n1,n2} from N tickets
Replies: 14   Last Post: Sep 25, 2012 1:34 AM

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Paul

Posts: 208
Registered: 2/23/10
Probability of selecting {n1,n2} from N tickets
Posted: Sep 23, 2012 1:59 AM
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In an example of the likelihood function, http://en.wikipedia.org/wiki/Likelihood_function#Example_2
describes an experiment in which two tickets are chosen from N tickets
numbered from n1 to nN. Given integers n1 and n2, with n2>n1, the
probability of selecting {n1,n2} is given as 1/(N choose 2). But
there are N ways to choose n1, and N-1 ways to choose n2; hence, there
are N(N-1) ways to choose {n1,n2} should be N(N-1), which is certainly
not (N choose 2). What am I missing?

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