00:01
For this exercise, we are told that the number of pieces of junk mail received in a day follows a poisson distribution with an average of 2 .6 per day.
00:13
And we are asked for the probability of receiving more than three pieces of junk mail in a given day.
00:22
So first, the probability function for the poisson random variable is given by this formula.
00:45
We want the probability of more than three.
00:48
So this is the probability that x is greater than 3, which is equal to 1 minus the probability that x is at most 3.
01:01
And the probability that x is at most 3 is equal to the probability that x equals 0, plus the probability that x equals 1, and so on, up to 3.
01:18
So that's 3 terms to solve using the probability function.
01:24
Each of these terms has a constant factor of e to the minus mu.
01:30
So let's factor that out right now...