1. 直接写出得数。
$ \frac{( )}{12} = \frac{2}{3} = 12 ÷ ( ) $
$ \frac{20}{( )} = 4 ÷ 5 = \frac{( )}{20} $
$ \frac{4}{9} + \frac{7}{9} = $
$ 16 ÷ 24 = \frac{32}{( )} = \frac{( )}{3} $
$ ( ) ÷ 20 = \frac{20}{( )} = \frac{1}{2} $
$ \frac{23}{24} - \frac{11}{24} = $
$ ( ) ÷ 16 = \frac{( )}{24} = \frac{7}{8} $
$ \frac{( )}{36} = \frac{4}{9} = 8 ÷ ( ) $
$ \frac{7}{19} + \frac{22}{19} = $
$ 9.8 - 0.89 = $
$ 5.8 - 3.2 = $
$ 1.25 × 50 = $
$ 2.5 + 0.64 + 0.36 = $
$ 2.4 × 0.5 = $
$ 0.75 × 4 = $
$ 10.4 ÷ 4 = $
$ 17.2 - 6.8 + 2.2 = $
$ 10 - 3.2 = $
$ 10.5 + 1.25 = $
$ 5.6 - 2.3 = $
$ 8.2 + 1.8 × 0.5 = $
$ 2.65 + 5.35 = $
$ 8.2 × 5 = $
$ 0.46 × 20 = $
$ 0.36 × 101 - 0.36 = $

1. 8 18 25 16 $\dfrac{11}{9}$ 48 2 10 40 $\dfrac{1}{2}$ 14 21 16 18 $\dfrac{29}{19}$ 8.91 2.6 62.5 3.5 1.2 3 2.6 12.6 6.8 11.75 3.3 9.1 8 41 9.2 36

2. 把下面各组分数通分。
$ \frac{3}{7} $$和$$ \frac{2}{5} $
$ \frac{8}{9} $$和$$ \frac{5}{12} $
$ \frac{13}{8} $$和$$ \frac{13}{9} $
$ \frac{1}{6} $$和$$ \frac{2}{9} $
$ \frac{7}{8} $$和$$ \frac{11}{24} $
$ \frac{7}{20} $$、$$ \frac{3}{10} $$和$$ \frac{7}{30} $

2. $\dfrac{15}{35}$ $\dfrac{14}{35}$ $\dfrac{32}{36}$ $\dfrac{15}{36}$ $\dfrac{117}{72}$ $\dfrac{104}{72}$ $\dfrac{3}{18}$ $\dfrac{4}{18}$ $\dfrac{21}{24}$ $\dfrac{11}{24}$ $\dfrac{21}{60}$ $\dfrac{18}{60}$ $\dfrac{14}{60}$

比较下面两组分数的大小。
(1)$ \frac{111}{1234} $和 $\frac{666}{7654}$ $(2) $$ \frac{2}{17} $$、$$ \frac{3}{21} $$和$$ \frac{6}{27} $

思维提升
（1）因为$\dfrac{111}{1234}=\dfrac{666}{7404}$，$\dfrac{666}{7404}＞\dfrac{666}{7654}$，所以$\dfrac{111}{1234}＞\dfrac{666}{7654}$。
（2）因为$\dfrac{2}{17}=\dfrac{6}{51}$，$\dfrac{3}{21}=\dfrac{6}{42}$，$\dfrac{6}{27}＞\dfrac{6}{42}＞\dfrac{6}{51}$，所以$\dfrac{6}{27}＞\dfrac{3}{21}＞\dfrac{2}{17}$。