I'm having trouble with this problem. I cannot figure out how to get the total number of possibilities of getting less than 9 stops. How would I go about calculating that value?
If there are 10 people and 40 floors, what is the probability that the elevator makes less than 9 stops?
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0Presumably the people independently and uniformly choose a destination floor. Do they choose it from $40$ floors or from $39$? Are they all starting on the same floor, so the $39$ they choose from are the same set? Many details need to be supplied before one can compute this reasonably. – 2017-01-27
1 Answers
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Use complementation.
You have 10 people selecting(how?), independently(?), from 40 destinations(or 39?).
You want the probability that they do not select 9 or 10 stops.