- #1

- 135

- 0

F(x) =

0 if x <-3

3/8 if -3 <= x < 0

1/2 if 0 <= x < 3

3/4 if 3 <= x <4

1 if x => 4

Calculate E(X) and E(X

^{2}- 2|X|)

Well I'm at a loss of E(X) although once I know this the other should be fairly simple..

Ive got E(X) = -3(3/8)-2(3/8)-1(3/8)+1(1/8)+2(1/8)+1(1/4)+2(1/4)+3(1/4)+4(1/4) = 5/8

Is this the right method?

Rather than making another post I also need a hand with the following.

Let X be the number of different birthdays among four persons selected randomly. Find E(X).

I know how to do this in principal E(X) = 0.p(0) + 1.p(1) + 2.p(2) + 3.p(3) + 4.p(4)

but i don't know how to find the probability mass function p(x) I know it will takes values 0,1,2,3,4 and will probably involve the pick formula 365!/(365-x)! or something along those lines.

Any help would be greatly appreciated!