# Math Help - Proof of joint variables

1. ## Proof of joint variables

There are two proofs in my books which they leave the proof to the reader, however i cannot seem to do this..
1) What are the conditional joint pmf of X1 and X2 given $X_j = s_j$ for all $3 <= j <= r$, where:
$(X_1, X_2,.....,X_{r-1})$ ~ $Multinomial (n,p_1, .... , p_{r-1})?$

Thank You

2. ## Re: Proof of joint variables

anyone please? Still cant seem to understand the question...