00:01
So here we're talking probability, right? and we've got this box and we have 13 and 7.
00:07
So the easiest way to do this is in steps, right? the probability that the first is defective, right, is just equal to 7 over 20.
00:20
Right? that's the odds.
00:21
But once we do that, then the box transforms because the next time, right, we have 13 and 6.
00:31
So the probability that the second is defective is going to be six over 19, because now there's only six defective ones left in the box, and there's a total of 19 left in the box.
00:46
And now we can invoke the multiplication rule, right? so the probability of a plus b is equal to the probability of a times the probability of b.
00:57
So on the first time we go, we have to do a 7 over 20...