p(6) = 0.0278, or about 1 chance in 36.Explanation
This is easily read off the Poisson Table, the p(6) row of the r = 2.5 column.
Note that this is a Poisson problem because we cannot meaningfully ask how many calls do not come in during that hour (you can find textbooks that attempt to make just that calculation, but those textbook writers are misguided). A phonecall is best conceived of as a random event out of nowhere. Anyone who has worked a switchboard during lunch hour will know what we mean.
Calls to a switchboard, or customers coming into a bank, are the classic Poisson "arrival" problem.
Statistics is Copyright © 2001- by E Bruce Brooks
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