00:01
So for this problem, to find our marginal probabilities, for instance, probability that y is equal to zero, we would take the sum of the conditional probabilities.
00:09
So probability that y equals zero, given that x equals 1, plus probability that y equals 0, given that x equals 2.
00:21
Or pardon me, let me correct myself here.
00:25
I shouldn't be saying those as conditional probabilities.
00:27
Rather, we would want to take the sum of the joint events, rather.
00:31
So, clear out leftovers from previous problem, there'd be 0 .15 plus 0 .3.
00:38
For a result of 0 .45 is the probability that y equals 0.
00:44
Probability that y equals 1, 0 .2 plus 0 .35 for results of 0 .55.
00:53
And similarly, we'd have that probability that x equals 0 is equal to 0 .15 plus 0 .2 for a result of 0 .35.
01:03
And probability that x equals 2 would be 0 .3, or pardon me, excuse me, that should be x equals 1 and x equals 2, excuse me, probability that x equals 2 is 0 .3 plus 0 .35 for a result of 0 .65.
01:22
And then for part b, to find the covariance of x and y, we can calculate by taking the expected value of x times y, minus the expected value of x times y, minus the expected value of x times the expected value of y.
01:40
So first to find the expected value of x times y, we want to take the sum of the probability that x and y take on each one, each of their possible values, multiplied by the product of those values.
01:58
So to be rigorous here, i'll be including the terms that would go to zero, but we'd have 0 .15 times 0 times 1, plus 0 .3 times 0 times 2, plus 0 .3 .2, plus 0 .4 .5 .5 .5 .5, plus 2 times 1 times 1 plus 0 .35 times 1 times 2...