1. 计算：
(1) $-20 - (-18) + (-14) + 13$.
(2) $(-33) - (-17) + (-15) - (+1) + (+23)$.
(3) $-\frac{3}{5} - \frac{1}{2} + \frac{3}{4} - \frac{2}{5} + \frac{1}{2} - \frac{7}{8}$.
(4) $4\frac{2}{3} + 2\frac{1}{5} - \frac{4}{5} + 2\frac{4}{5} - (-6\frac{1}{3})$.

(1) 原式$=-20+18-14+13=(-20-14)+(18+13)=-34+31=-3$.
(2) 原式$=-33+17-15-1+23=(-33-15-1)+(17+23)=-49+40=-9$.
(3) 原式$=(-\frac{3}{5}-\frac{2}{5})+(-\frac{1}{2}+\frac{1}{2})+(\frac{3}{4}-\frac{7}{8})=-1+0-\frac{1}{8}=-1\ \frac{1}{8}$.
(4) 原式$=(4\ \frac{2}{3}+6\ \frac{1}{3})+(2\ \frac{1}{5}-\frac{4}{5}+2\ \frac{4}{5})=11+4\ \frac{1}{5}=15\ \frac{1}{5}$.

2. 计算：
(1) $(+6.6)+(-5.2)-(-3.8)+(-2.6)-(+4.8)$。
(2) $28\frac{3}{5}+(-18\frac{1}{4})-(+1\frac{1}{3})+0.25-(-3\frac{2}{3})+(-2\frac{1}{3})-10\frac{3}{5}$。
(3) $(-1.25)×\frac{5}{7}×(-4)×(-\frac{7}{5})$。

(1) 原式$=6.6-5.2+3.8-2.6-4.8=(6.6-2.6)+(-5.2-4.8)+3.8=4-10+3.8=-6+3.8=-2.2$.
(2) 原式$=(28\ \frac{3}{5}-10\ \frac{3}{5})+[(-18\ \frac{1}{4})+0.25]-[1\ \frac{1}{3}+(-3\ \frac{2}{3})+2\ \frac{1}{3}]=18-18-0=0$.
(3) 原式$=[(-1.25)×(-4)]×[\frac{5}{7}×(-\frac{7}{5})]=5×(-1)=-5$.

3. 计算：$(-0.75)+3\dfrac{4}{9}+\left|-\dfrac{3}{4}\right|+(-5\dfrac{1}{2})+\left|-2\dfrac{5}{9}\right|.$

原式$=-\frac{3}{4}+3\ \frac{4}{9}+\frac{3}{4}-5\ \frac{1}{2}+2\ \frac{5}{9}=(-\frac{3}{4}+\frac{3}{4})+(3\ \frac{4}{9}+2\ \frac{5}{9})-5\ \frac{1}{2}=0+6-5\ \frac{1}{2}=\frac{1}{2}$.