Answer:
(a) The probability that a text message user receives or sends three messages per hour is 0.2180.
(b) The probability that a text message user receives or sends more than three messages per hour is 0.2667.
Step-by-step explanation:
Let <em>X</em> = number of text messages receive or send in an hour.
The random variable <em>X</em> follows a Poisson distribution with parameter <em>λ</em>.
It is provided that users receive or send 62.7 text messages in 24 hours.
Then the average number of text messages received or sent in an hour is:
.
The probability of a random variable can be computed using the formula:
![P(X=x)=\frac{e^{-\lambda}\lambda^{x}}{x!} ;\ x=0, 1, 2, 3, ...](https://tex.z-dn.net/?f=P%28X%3Dx%29%3D%5Cfrac%7Be%5E%7B-%5Clambda%7D%5Clambda%5E%7Bx%7D%7D%7Bx%21%7D%20%3B%5C%20x%3D0%2C%201%2C%202%2C%203%2C%20...)
(a)
Compute the probability that a text message user receives or sends three messages per hour as follows:
![P(X=3)=\frac{e^{-2.6125}(2.6125)^{3}}{3!} =0.21798\approx0.2180](https://tex.z-dn.net/?f=P%28X%3D3%29%3D%5Cfrac%7Be%5E%7B-2.6125%7D%282.6125%29%5E%7B3%7D%7D%7B3%21%7D%20%3D0.21798%5Capprox0.2180)
Thus, the probability that a text message user receives or sends three messages per hour is 0.2180.
(b)
Compute the probability that a text message user receives or sends more than three messages per hour as follows:
P (X > 3) = 1 - P (X ≤ 3)
= 1 - P (X = 0) - P (X = 1) - P (X = 2) - P (X = 3)
![=1-\frac{e^{-2.6125}(2.6125)^{0}}{0!}-\frac{e^{-2.6125}(2.6125)^{1}}{1!}-\frac{e^{-2.6125}(2.6125)^{2}}{2!}-\frac{e^{-2.6125}(2.6125)^{3}}{3!}\\=1-0.0734-0.1916-0.2503-0.2180\\=0.2667](https://tex.z-dn.net/?f=%3D1-%5Cfrac%7Be%5E%7B-2.6125%7D%282.6125%29%5E%7B0%7D%7D%7B0%21%7D-%5Cfrac%7Be%5E%7B-2.6125%7D%282.6125%29%5E%7B1%7D%7D%7B1%21%7D-%5Cfrac%7Be%5E%7B-2.6125%7D%282.6125%29%5E%7B2%7D%7D%7B2%21%7D-%5Cfrac%7Be%5E%7B-2.6125%7D%282.6125%29%5E%7B3%7D%7D%7B3%21%7D%5C%5C%3D1-0.0734-0.1916-0.2503-0.2180%5C%5C%3D0.2667)
Thus, the probability that a text message user receives or sends more than three messages per hour is 0.2667.