00:01
We are looking at a binomial distribution here.
00:03
It needs two parameters.
00:06
N, the number of trials, is 9.
00:08
P, the probability of success, is 0 .2.
00:12
We use the probability, x, the number of successes, is 3 or fewer.
00:18
Or equal or less than? no, actually, i think it is just less than.
00:24
Okay, less than 3.
00:26
So i'm going to use the binomial formula.
00:29
You could also use distribution tables with these parameters or technology.
00:33
The probability exactly x successes occur is n choose x p to the x or minus p to the n minus x.
00:42
Now we want less than three.
00:45
That could be 0, 1 or 2.
00:48
I need to find those probabilities and add them up.
00:51
We'll start with 2.
00:52
The important point is that these trials are independent of each other, which means you combine them by this multiplying.
00:59
This term is for the successes, each a probability of 0 .2, multiply that by itself, two times...