# plz help in finding Expectation and Covariance

• Mar 27th 2010, 05:32 AM
goaway716
plz help in finding Expectation and Covariance
Finding 6 coins in his pocket, Aloysius proposes a game of chance. He will toss all 6 coins; let X denote the number of heads obtained. Persephone will then toss all the coins which came up tails when Aloysius tossed them. Let Y denote the number of heads Persephone obtains.

1)Calculate the expectation of Y.
2)Write down the conditional probability function of X given that Y = 3.
3)Explain why you would expect the covariance between X and Y to be negative.
4)Calculate Cov(X, Y) and ρX,Y.
5)Persephone will pay Aloysius £1 for every Head Aloysius manages to obtain; Aloysius will pay Persephone £2 for every Head Persephone gets. Let Z represent Aloysius' net profit from one game. Calculate the expectation and variance of Z
• Mar 27th 2010, 11:55 PM
CaptainBlack
Quote:

Originally Posted by goaway716
Finding 6 coins in his pocket, Aloysius proposes a game of chance. He will toss all 6 coins; let X denote the number of heads obtained. Persephone will then toss all the coins which came up tails when Aloysius tossed them. Let Y denote the number of heads Persephone obtains.

1)Calculate the expectation of Y.
2)Write down the conditional probability function of X given that Y = 3.
3)Explain why you would expect the covariance between X and Y to be negative.
4)Calculate Cov(X, Y) and ρX,Y.
5)Persephone will pay Aloysius £1 for every Head Aloysius manages to obtain; Aloysius will pay Persephone £2 for every Head Persephone gets. Let Z represent Aloysius' net profit from one game. Calculate the expectation and variance of Z

Label the coins \$\displaystyle 1\$ to \$\displaystyle 6\$, the probability \$\displaystyle p_i\$ that P gets a head with coin \$\displaystyle i\$ is that came up tails for A and heads for P, that is \$\displaystyle p_i=1/4\$.

So the number of heads that P gets from the \$\displaystyle 6\$ initial coins \$\displaystyle Y\sim B(6,1/4)\$

CB