Question

Consider a Poisson probability distribution with λ = 2.8. Determine the following probabilities.

a) P(x = 5)
b) P(x > 6)
c) P(x ≤3)

Answer 1

a) Using the Poisson probability formula:

P(x = 5) = (e^(-λ) * λ^x) / x!

P(x = 5) = (e^(-2.8) * 2.8^5) / 5!

P(x = 5) ≈ 0.1008

b) P(x > 6) = 1 - P(x ≤ 6)

We can find P(x ≤ 6) using the cumulative Poisson probability formula:

P(x ≤ 6) = Σ (e^(-λ) * λ^x) / x!

P(x ≤ 6) = (e^(-2.8) * 2.8^0) / 0! + (e^(-2.8) * 2.8^1) / 1! + (e^(-2.8) * 2.8^2) / 2! + (e^(-2.8) * 2.8^3) / 3! + (e^(-2.8) * 2.8^4) / 4! + (e^(-2.8) * 2.8^5) / 5! + (e^(-2.8) * 2.8^6) / 6!

P(x ≤ 6) ≈ 0.8581

Therefore,

P(x > 6) = 1 - P(x ≤ 6)

P(x > 6) ≈ 0.1419

c) P(x ≤ 3) = Σ (e^(-λ) * λ^x) / x!

P(x ≤ 3) = (e^(-2.8) * 2.8^0) / 0! + (e^(-2.8) * 2.8^1) / 1! + (e^(-2.8) * 2.8^2) / 2! + (e^(-2.8) * 2.8^3) / 3!

P(x ≤ 3) ≈ 0.4232