1. 直接写出得数。
$ \frac{2}{15} + \frac{1}{5} = $$ $$ \frac{1}{7} - \frac{1}{14} = $$ $$ \frac{8}{9} + \frac{2}{3} = $$ $$ \frac{5}{6} - \frac{7}{20} + \frac{1}{15} = $
$ 108 × \frac{7}{18} = $$ $$ \frac{5}{24} × 120 = $$ $$ \frac{5}{6} × 12 = $$ $$ \frac{29}{42} × \frac{56}{87} × \frac{2}{3} = $
$ \frac{4}{15} × \frac{5}{12} = $$ $$ \frac{11}{7} × \frac{7}{11} = $$ $$ \frac{17}{36} × \frac{72}{85} = $$ $$ \frac{4}{9} × \frac{9}{28} × 5 = $
$ \frac{5}{6} × \frac{4}{5} = $$ $$ \frac{3}{8} × \frac{2}{15} = $$ $$ \frac{5}{6} × \frac{9}{20} = $$ $$ \frac{17}{24} × \frac{3}{34} × \frac{2}{3} = $
$ \frac{3}{8} × \frac{4}{9} = $$ $$ \frac{1}{3} × \frac{30}{31} = $$ $$ \frac{4}{11} × \frac{33}{28} = $$ $$ \frac{16}{3} × \frac{3}{32} × \frac{5}{3} = $
$ \frac{1}{19} × \frac{38}{3} = $$ $$ \frac{5}{7} × \frac{21}{2} = $$ $$ \frac{5}{36} × 20 = $$ $$ \frac{9}{10} × \frac{25}{18} × \frac{5}{4} = $

1. $\frac{1}{3}$ $\frac{1}{14}$ $\frac{14}{9}$ $\frac{11}{20}$
42 25 10 $\frac{8}{27}$
$\frac{1}{9}$ 1 $\frac{2}{5}$ $\frac{5}{7}$
$\frac{2}{3}$ $\frac{1}{20}$ $\frac{3}{8}$ $\frac{1}{24}$
$\frac{1}{6}$ $\frac{10}{31}$ $\frac{3}{7}$ $\frac{5}{6}$
$\frac{2}{3}$ $\frac{15}{2}$ $\frac{25}{9}$ $\frac{25}{16}$

2. 计算下面各题。
$ \frac{5}{7} × \frac{28}{13} × \frac{2}{7} $$ $$ \frac{2}{3} × \frac{13}{8} × \frac{4}{39} $$ $$ \frac{19}{20} × \frac{4}{9} × \frac{25}{38} $
$ \frac{3}{8} × \frac{7}{9} × \frac{16}{21} $$ $$ \frac{3}{7} × \frac{2}{5} × \frac{35}{12} $$ $$ \frac{8}{15} × \frac{5}{16} × \frac{3}{4} $

2. $\frac{40}{91}$ $\frac{1}{9}$ $\frac{5}{18}$
$\frac{2}{9}$ $\frac{1}{2}$ $\frac{1}{8}$

已知$ \frac{1}{3} △ 2 = \frac{1}{3} × \frac{1}{4} ，$$ \frac{1}{9} △ 3 = \frac{1}{9} × \frac{1}{10} × \frac{1}{11} ，$那么$ \frac{1}{2} △ 4 - \frac{1}{3} △ 4 $的值是$($　　$)。$　　

思维提升
$\frac{1}{180}$