1. (3 points) Calculate: $100-99+98-97+96-95+94-93+93-92+91=$
【Solution】Solution: $100-99+98-97+96-95+94-93+93-92+91$,
$$
\begin{array}{l}
=(100-99)+(98-97)+(96-95)+(94-93)+(93-92)+91, \\
=1 \times 5+91, \\
=5+91, \\
=96 .
\end{array}
$$

Therefore, the answer is: 96.