Paper 2, Section I, F

Probability | Part IA, 2014

Consider independent discrete random variables X1,…,XnX_{1}, \ldots, X_{n} and assume E[Xi]E\left[X_{i}\right] exists for all i=1,…,ni=1, \ldots, n.

Show that

E[∏i=1nXi]=∏i=1nE[Xi]E\left[\prod_{i=1}^{n} X_{i}\right]=\prod_{i=1}^{n} E\left[X_{i}\right]

If the X1,…,XnX_{1}, \ldots, X_{n} are also positive, show that

∏i=1n∑m=0∞P(Xi>m)=∑m=0∞P(∏i=1nXi>m)\prod_{i=1}^{n} \sum_{m=0}^{\infty} P\left(X_{i}>m\right)=\sum_{m=0}^{\infty} P\left(\prod_{i=1}^{n} X_{i}>m\right)

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