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I am trying to study probability theory by myself. I asked myself a question about expectation, and I have no idea how to solve it. Please help me with solution and my understanding. The question I asked is following: Let $a, b, c, d$ be non-negative natural numbers, say from the set $\{0, 1, ..., n\}.$ Calculate the expectation $$ E\left( (-1)^{a+b+c+d}\right). $$

Thank you for your help.

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    You should say something about the probability distribution of your four random variables $a,b,c,d$.2012-02-29

1 Answers 1