00:03
Okay, this question tells us that a company gets its vials from company x, one -fifth of the time, and other companies four -fifths of the time.
00:18
And it gives the different failure rate for each company.
00:23
And it wants us to find a sample of 30 vials where one is ineffective, and it wants us to know the probability that it came from x.
00:49
To do this, i'll draw a tree diagram, so you can either order from company x, one -fifth at a time, or you could order from others, four -fifths at the time.
01:09
And then from there, we know one out of 30 vials is defective, so we need to find each of these probabilities.
01:35
And we can do this using the binomial formula.
01:38
We want the probability of exactly one fail out of 30.
01:46
So we have 30 choose one times the probability of failure in our case, which is different for company x and y.
02:06
So i'm just going to write it like this, because we have one success and 29 fails, where a success is a bad file...