Wow, ok nevermind:
We know \sum x_n converges.
|yn| <= M, For any n contained in the naturals - Def of bounded.
Then,
\sum x_n y_n = \sum \left|x_n\right| \left|y_n\right| \leq M\sum \left|x_n\right|
Therefore, the sum converges!
A counter example would be to let xn =...