Answer
a) You cannot say anything about $\Sigma a_{n}$
b) $\Sigma a_{n}$ is convergent
Work Step by Step
a) You cannot say anything about $\Sigma a_{n}$, as you need either $a_{n} < b_{n}$ or $\Sigma b_n$ divergent to use the comparison test.
b) Given $a_{n} < b_{n}$ for all $n$ & $\Sigma b_{n}$ is convergent, it follows that $\Sigma a_{n}$ is convergent by the Comparison Test.
