# Conditional Epectation of Multinomial

## Main Question or Discussion Point

So I'm trying to find E(X1,X2|Xn) where X1,X2,.....Xn are the numbers of cell observations in a multinomial distribution.

How do I even calculate this? I know it is not independent so I cannot split it.

Does it have something to do with the fact that E(Xi)=nPi ?

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Stephen Tashi
Intuitively, we would expect the distribution of $(X1, X2| Xn = 6)$ to be a multinomial distribution for 6 less objects with the cell probabilities for $X1, X2,..X[n-1]$ scaled by a factor so they sum to 1. I don't know what your notation $E(X1,X2...$ means. Are you asking about a vector of expectations?
Intuitively, we would expect the distribution of $(X1, X2| Xn = 6)$ to be a multinomial distribution for 6 less objects with the cell probabilities for $X1, X2,..X[n-1]$ scaled by a factor so they sum to 1. I don't know what your notation $E(X1,X2...$ means. Are you asking about a vector of expectations?