# conditional variance

1. ### Binomial expectation E(X|X>1)

General case: X~B(n,p) I could integrate the product of x and pmf from 1 to infinity and divide it by the integral of just pmf from 1 to infinity to find it, but I'm really stuck since I can't do it due to the sophisticated pmf function of binomial. How can we find this expectation and...
2. ### Conditional Variance

Hi, I have difficulty understanding the definition of conditional variance as: var(X|Y) = E[(X-E[X|Y])**2 | Y]. Given the definition of variance of a random variable X: var(X) = E[(X-E[X])**2], and substituting X with X|Y, you get: var(X|Y) = E[(X|Y-E[X|Y])**2]. How can one get from this...