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Probability / Statistics question

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Z-Juice
Posts: 3151 - Karma: 1,504
Hopefully you guys can help me out with a fairly simple statistics problem:

Three fair dice are rolled together. Let X be the random variable denoting the sum of all three top faces. Write out the pmf and cdf.

I know what a pmf and cdf are, but all of the examples in class and other problems we've done have been done knowing what the pmf and cdf are and then computing the probabilities of X. I'm having trouble approaching this problem because it's the other way around.
Feb 12 2015 11:04AM
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Yaraelpoof.png
Posts: 1556 - Karma: 6,418
Find q? And do it that way?
Feb 12 2015 11:22AM
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TurquoiseGrizzly
Posts: 1819 - Karma: 13,149
Skiing is always the answer
Feb 12 2015 11:49AM
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Lus146
Posts: 422 - Karma: 2,282
Speak english please.
Feb 12 2015 12:01PM
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Blurst
Posts: 13577 - Karma: 10,169
MrGnarlsonSkiing is always the answer


I completely and whole heartedly agree, OP should certainly go skiing to alleviate the problem.
Feb 12 2015 12:19PM
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Z-Juice
Posts: 3151 - Karma: 1,504
BlurstI completely and whole heartedly agree, OP should certainly go skiing to alleviate the problem.


That's the plan if I can get this assignment done.
Feb 12 2015 12:27PM
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Z-Juice
Posts: 3151 - Karma: 1,504
Mr.SaltyFind q? And do it that way?


I don't know what q is, and this question is not supposed to be very complicated. Out of the few distributions we've learned (Geometric, Bernoulli, Binomial, Poisson), I think you just need to pick one to find which models the individual results of each die, which is your pmf, and then integrate the pmf to get the cdf. I'm confused because the Geometric, Bernoulli, and Binomial distributions only model "successes or failures", no more than two options while you can roll a 1,2,3,4,5 or 6 with a die.
Feb 12 2015 12:35PM
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DrZoidberg
Posts: 5675 - Karma: 4,268
I haven't done this in a while, especially not in this context. But it's a bernoulli thing right?

http://en.wikipedia.org/wiki/Multinomial_distribution

Could be totally wrong. I never really did this much in this sort of problem.
Feb 12 2015 6:38PM
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