G285 2021 Fall Problem Set Problem 8

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Problem

If the value of \[\sum_{a=1}^{\infty} \sum_{b=1}^{\infty} \sum_{c=1}^{\infty} \frac{a+2b+3c}{4^(a+b+c)}\] can be represented as $\frac{m}{n}$, where $m$ and $n$ are relatively prime. Find $m+n$.

Solution

Geometric series spam