Suppose the number of messages that an inbox receives may be modeled by a Poisson distribution. If the average number of messages per hour is 18, then what is the probability it will receive between 15 and 20 messages during any given hour?

0.36427

Step-by-step explanation:

Mean = λ = 18 messages per hour

P(X = x) = (e^-λ)(λ⁻ˣ)/x!

P(X ≤ x) = Σ (e^-λ)(λ⁻ˣ)/x! (Summation From 0 to x)

But the probability required is that the messages thay come in an hour is between 15 and 20, that is, P(15 < X < 20)

P(15 < X < 20) = P(X < 20) - P(X ≤ 15)

These probabilities will be evaluated using a cumulative frequency calculator.

P(X < 20) = 0.65092

P(X ≤ 15) = poissoncdf(18, 15) = 0.28665

P(15 < X < 20) = P(X < 20) - P(X ≤ 15) = 0.65092 - 0.28665 = 0.36427.

You can use the Poisson distribution calculator here

https://stattrek.com/online-calculator/poisson.aspx

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