00:01
We're a number problem 16.
00:02
So it says three cds are picked at random from 12 cds, four of which are defective.
00:08
What's the probability of the following? all three cds are defective.
00:14
So let's think about this.
00:19
All right.
00:20
So there are 12 cds and i just say red for bad.
00:28
And four cds are bad.
00:33
So let's draw a frowny face.
00:39
Okay.
00:40
And what's the probability of the following? all three cds are selected.
00:46
So we're going to have three choosing of the cds.
00:55
And i guess in this problem, we are assuming that we are not going to replace.
01:01
So first, we're going to choose one cd, and we must assume that it's effective because that's the problem.
01:09
So we have probability of choosing the first cd being defective is 4 over 12.
01:17
Assuming that happens, the probability of choosing another defective cd will be 3 over 11.
01:27
The reason why 12 becomes 11 is because we are not going to put the cd back when we choose these cds...