Let X be distribution over N (the set of non-negative numbers), with mass P(X=i) = a/2^i, what is the value of a?

Question

I am struggling with solution for following problem part of course about probabilities random variables, seek your kind help to show how to solve it,

Let $X$ be distribution over $N$ (the set of non-negative numbers), with mass $P(X=i) = a/2^i$, what is the value of $a$?

Answer 1

Hint: $\sum_{i=0}^{\infty}\dfrac{a}{2^i}=1$, can you sum the series?