## kirbykirby 2 years ago 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 ._.