Answer
The $(n+1)$th partial sum is obtained by adding a positive number to the $n$th partial sum
Work Step by Step
Let $\sum a_k$ be a series of positive terms and $S_n=\sum_{k=1}^n$ the $n$th partial sum.
$S_{n+1}=\sum_{k=1}^{n+1} a_k=\sum_{k=1}^{n} a_k+a_{n+1}=S_n+a_{n+1}$
As $a_{n+1}>0$, it means that $S_{n+1}>S_n$, therefore the sequence of partial sums is an increasing sequence.
