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Molecules are emitted in a rate which distribute poisson(0.5). (0.5 molecule per/second rate).

calculate the probabilities:

  1. At least one molecule will be emitted in a certain second.
  2. More than 3 molecules will be emitted within 5 seconds.

thanks.

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Looks a lot like a homework problem, and if so, please add the homework tag. Also, what are your thoughts on the matter? Where are you stuck? –  Dilip Sarwate Jan 23 '13 at 15:47

1 Answer 1

up vote 2 down vote accepted

The number of molecules emitted in a second has Poisson distribution, parameter $0.5$.

The probability of at least one molecule is $1$ minus the probability of $0$ molecules.

The probability of $0$ molecules is $e^{-0.5}$.

For the $5$ second problem, use the fact that the number of molecules in a $5$ second interval has Poisson distribution with parameter (mean) equal to $(0.5)(5)$.

To find the probability of more than $3$ molecules, first find the probability of $3$ or fewer molecules. This will involve adding four terms.

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