2018年IMAS小学中年级竞赛（第二轮）第1题4分
请问$$100-97+94-91+88-85+\cdots +4-1$$之值等于多少？ 
拓展思维->拓展思维->计算模块->数列与数表->数列规律
$$100-97+94-91+88-85+\cdots +4-1$$  $$=\left( 100-97 \right)+\left( 94-91 \right)+\left( 88-85 \right)+\cdots +\left( 4-1 \right)$$  $$=\underbrace{3+3+3+\cdots +3}_{17项}$$  $$=3\times 17$$  $$=51$$．  故选$$\text{C}$$．  <p>$$100-97+94-91+88-85+\cdots +4-1$$</p>
<p>$$=\left( 100+94+88+\cdots +4 \right)-\left( 97+91+85+\cdots +1 \right)$$</p>
<p>$$=\frac{\left( 100+4 \right)\times 17}{2}-\frac{\left( 97+1 \right)\times 17}{2}$$</p>
<p>$$=\left( 104-98 \right)\times \frac{17}{2}$$</p>
<p>$$=6\times \frac{17}{2}$$</p>
<p>$$=51$$．</p>
<p>故选$$\text{C}$$．</p>