Question

The number of text messages sent daily by a student is a poisson random variable with parameter λ=5 .in a class with 20 independent students, what is the probability that in a given day every student sends less than 6 messages?

Answer 1

This problem is a combination of the Poisson distribution and binomial distribution.

First, we need to find the probability of a single student sending less than 6 messages in a day, i.e.
P(X<6)=P(X=0)+P(X=1)+P(X=2)+P(X=3)+P(X=4)+P(X=5)
=0.006738+0.033690+0.084224+0.140374+0.175467+0.175467
= 0.615961

For ALL 20 students to send less than 6 messages, the probability is
P=C(20,20)*0.615961^20*(1-0.615961)^0
=6.18101*10^(-5)   or approximately
=0.00006181