1 [2026 浙江杭州调研,中]计算:(1)$(+7)+(-21)+(-7)+(+21)$;
(2)$(-2)+(+3)+(+4)+(-3)+(+5)+(-4)$.

1.【解】(1)原式$=[7+(-7)]+[(-21)+21] = 0+0=0$.
(2)原式$=[(-2)+(+5)]+[(+3)+(-3)]+[(+4)+(-4)] = 3+0+0=3$.

2[2026浙江温州质检,中]计算:(1)$(-23.7)+58+(-16.3)+22$；
(2)$(-2 \frac{1}{8})+(-3 \frac{1}{2})+(+5)+(+1.125)+(+4 \frac{1}{2})$

2.【解】(1)原式$=[(-23.7)+(-16.3)]+(58+22) = -40+80=40$.
(2)原式$=(-2. 125)+(-3. 5)+5+1. 125+4. 5 = [ (-2. 125)+1. 125 ] + [ (-3. 5)+4. 5 ] + 5 = (-1)+1+5=5$.

3[2026江苏南通期末,中]计算:(1)$2+(-3)+(+4)+(-5)+6$；
(2)$(-17)+23+(-53)+(+36)$.

3.【解】(1)原式$=(2+4+6)+[(-3)+(-5)] = 12+(-8)=4$.
(2) 原式 = [ ( - 17 ) + ( - 53 ) ] + [ 23 + (+36) ] = -70+59=-11.

4[2026北京西城区质检,中]计算:(1)$(-\dfrac{3}{7})+(+\dfrac{1}{5})+(+\dfrac{2}{7})+(-1\dfrac{1}{5})$；
(2)$2\dfrac{3}{4}+5\dfrac{2}{3}+(-2.75)+(-5\dfrac{1}{3})$。

4.【解】(1) 原式 = $[(-\frac{3}{7})+\frac{2}{7}] + [ \frac{1}{5} + (-1 \frac{1}{5}) ] = -\frac{1}{7}+(-1) = -1 \frac{1}{7}$.
(2)$2\ \frac{3}{4}+5\ \frac{2}{3}+(-2.75)+(-5\ \frac{1}{3}) = 2\ \frac{3}{4}+5\ \frac{2}{3}+(-2\ \frac{3}{4})+(-5\ \frac{1}{3}) = [ 2\ \frac{3}{4}+(-2\ \frac{3}{4}) ] + [ 5\ \frac{2}{3}+(-5\ \frac{1}{3}) ] = 0+\frac{1}{3} = \frac{1}{3}$.

5[2026浙江嘉兴期中,中]计算:$1+3+5+7+9+\dots+95+97+99.$

5.【解】$1+3+5+7+9+\dots+95+97+99$
$=(1+99)+(3+97)+(5+95)+\dots+(49+51)$
$=100+100+100+\dots+100$
$=100×50÷2$
$=5\ 000÷2=2\ 500$.