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Old 07-31-2007   #1
ray2won
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Question probability problem

Hello!
I cann't think out this problem.Please help me.ok?
There is a possible stop at every floor(floor 3,floor 2 and floor 1).Assume that any person is likely to get off at any floor and let X be the number of people that get off on the first floor.
(i)What values can X take on?
(ii)Find the probability for each possible value of X.
(iii) What is the expected number of people getting off on the first floor?
 
Old 07-31-2007   #2
Sillysidley

 
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Doesn't it depend on how many people there are? Well, I guess I'll let that be Y. Also, I assume you start at the floor below the first.
(i) The possible values range from 0 to Y
(ii) For 0- Basically each person has a chance of not going off at floor 1, and there are X people.
Similarly, for 1 (I'm kind of guessing on this) it's . ( Or should that be multiplied by Y?)That's a hint, I don't want to do it all, so the rest is yours
(iii)You expect of the poeple to get off at each floor, so the answer is

Hopefully I got some of these right...
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Last edited by Sillysidley; 07-31-2007 at 06:10 PM.. Reason: Thought it was AoPS...
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Old 08-01-2007   #3
Scion

 
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I wouldn't be helping much since somedude and i share the same answers. Lets say there are Y people.
1)If they have an equal chance of getting off the answer to this would simply be anywhere from 0 to Y(sidenote: if i said between 0 and Y that would not include 0 and Y).
2)I thought when you kind of answered the question in the information given since they have an equal chance so everything would have a chance since theres an equal probability.
3)straight-forward this is because if theres an equal chance we would expect equal people to get off at each floor and since there are Y people the answer was .
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Old 08-01-2007   #4
Sillysidley

 
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I don't agree with your number two. Out of the Y people, each one has a probability of going to floor one and a chance of not going on floor one. The only thing I'm not sure of, is since we choose 1 of the people to be on floor one, I think we might have to multiply by Y since we have Y ways to choose that Y person...
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Last edited by Temperal; 08-01-2007 at 05:46 PM.. Reason: LaTeX
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Old 08-01-2007   #5
Temperal
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Haha, forgot we're not on AoPS, did you, Siddhant?
 
Old 08-01-2007   #6
Sillysidley

 
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Yeah, same thing happened on my old post... thanks for fixing it
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