00:01
You actually have three questions in one here.
00:02
So that first question, we know that the probability of a is 0 .65, and the probability of b is given to be 0 .77.
00:13
And the probability of at least one of them, which means at least one means a or b is equal to 0 .9.
00:22
And so we want to find the probability of a and b.
00:26
We want to find are they mutually exclusive and we want to find are they independent? and so we know this statement is true for all union events.
00:40
Probability of a or b is equal to the probability of a plus the probability of b minus the probability of the a and b.
00:49
And so we know 0 .9 is equal to 0 .65 plus 0 .44 minus the intersection of these two, which is what we want to find of a and b.
01:04
And so doing our algebra on this, basically i'll end up, if i get this on this side, i'll get that probability of a and b equaling 0 .65 plus 0 .77 minus 0 .9.
01:20
And 0 .65 plus 0 .77 minus 0 .9 gives me a total of 0 .52 .6 .5.
01:28
So the intersection of those is .52, which means, no, they're not mutually exclusive because they can happen at the same time.
01:37
Independent, well, our test for independent is, let's find what the product is of these two.
01:44
Because if the product of these two, the 0 .65 times .77, if that product, that product is .505, and that does not equal the probability of the intersection.
01:56
So no, they're not independent.
01:58
They're not far from it, but they are not independent.
02:02
Now, question two.
02:04
Question two, you were dealing with passing, and the probability of passing first class is 0 .835.
02:13
Probability of passing, well, we want to find that.
02:17
Probability of passing both classes is 0 .276, and the probability of passing at least one of them, which means a or b.
02:31
So at least one means you either pass a or b or possibly both, and that's 0 .981.
02:37
And we have exactly the same scenario.
02:39
We want to use that union formula.
02:42
So 0 .981 is equal to the probability of a plus the probability of b, which we don't know, minus the intersection, which is this 0 .76.
02:55
So if we take the .981 and subtract away .835 and add, we'll get that to the other side that's adding on, add on, oops i didn't put the right symbol in there.
03:10
I got to insert a subtraction, otherwise we're going to have an issue.
03:14
And then add on the .276.
03:20
.276.
03:21
And that comes out to be the probability of b is equal to point 422.
03:28
So there's your first answer.
03:30
And then we wanted to find out are they mutually exclusive? and the answer is no.
03:35
Before there's an intersection...