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kirbykirby
Given the following pmf (prob. mass function), find its cdf: \[f(x)=\frac{7}{10}(\frac{3}{10})^x, x=0,1,2,...\]
I know for a discrete r.v., the formula for the cdf is: \[F(x)=\sum_{X_j \le X}^{}f(x_j)\], but I am having trouble with this ._.