1. 计算：
(1) $-3.19 + 2\dfrac{19}{21} + (-6.81) - (-2\dfrac{2}{21})$
(2) $(-2\dfrac{1}{8}) + (+5) + (-3\dfrac{1}{2}) + (+1.125) + (+4\dfrac{1}{2})$

(1) 原式$=-3.19+2\dfrac{19}{21}+(-6.81)+2\dfrac{2}{21}=[-3.19+(-6.81)]+(2\dfrac{19}{21}+2\dfrac{2}{21})=-10+5=-5$.
(2) 原式$=(-2\dfrac{1}{8})+5+(-3\dfrac{1}{2})+1\dfrac{1}{8}+4\dfrac{1}{2}=[(-2\dfrac{1}{8})+1\dfrac{1}{8}]+5+(-3\dfrac{1}{2}+4\dfrac{1}{2})=-1+5+1=5$.

2. 计算：
(1) $5 + (-4) + 6 + 4 + 3 + (-3) + (-2)$。
(2) $(-2.125) + (+3\dfrac{1}{5}) + (+5\dfrac{1}{8}) + (-3.2)$。

(1) 原式$=[(-4)+4]+[5+(-3)+(-2)]+6+3=6+3=9$.
(2) 原式$=[(-2.125)+5\dfrac{1}{8}]+[3\dfrac{1}{5}+(-3.2)]=3+0=3$.

3. 计算：
(1) $-99\frac{98}{99} × 198$.
(2) $25 × \frac{3}{4} - (-25) × \frac{1}{2} + 25 × (-\frac{1}{4})$.
(3) $2 × (-\frac{4}{9}) + 1.53 × \frac{4}{9} - 9.47 × (-\frac{4}{9}) - (\frac{7}{9} - \frac{5}{6} + \frac{1}{4} - \frac{1}{18}) × 72$.

(1) 原式$=(-100+\dfrac{1}{99})×198=-100×198+\dfrac{1}{99}×198=-19\ 800+2=-19\ 798$.
(2) 原式$=25×\dfrac{3}{4}+25×\dfrac{1}{2}-25×\dfrac{1}{4}=25×(\dfrac{3}{4}+\dfrac{1}{2}-\dfrac{1}{4})=25×1=25$.
(3) 原式$=(2-1.53-9.47)×(-\dfrac{4}{9})-(\dfrac{7}{9}×72-\dfrac{5}{6}×72+\dfrac{1}{4}×72-\dfrac{1}{18}×72)=4-10=-6$.