Solution
= Solution
Group consecutive terms in pairs. The $j$th pair, for $j=1,\ldots,25$, is
$$
-\frac{4j-3}{2}+\frac{4j-1}{2}=1.
$$
There are $25$ such pairs in this finite <sum>, so the answer is $\boxed{25}$.
= Solution
Group consecutive terms in pairs. The $j$th pair, for $j=1,\ldots,25$, is
$$
-\frac{4j-3}{2}+\frac{4j-1}{2}=1.
$$
There are $25$ such pairs in this finite <sum>, so the answer is $\boxed{25}$.