一、口算。
$\frac {5}{7}×\frac {21}{25}=$ $9÷\frac {6}{7}=$ $\frac {3}{7}×21=$
$\frac {1}{6}+\frac {1}{9}=$ $\frac {2}{17}÷\frac {8}{17}=$ $\frac {8}{3}×\frac {3}{10}=$
$\frac {5}{6}÷\frac {5}{17}=$ $\frac {1}{3}×\frac {9}{20}=$ $\frac {6}{5}-\frac {3}{8}=$
$\frac {3}{4}÷\frac {1}{4}=$ $\frac {2}{5}+\frac {4}{25}=$ $\frac {1}{12}×\frac {4}{7}=$
$2×\frac {2}{3}=$ $\frac {7}{18}÷\frac {5}{9}=$ $\frac {7}{8}+\frac {1}{6}=$
$\frac {4}{15}÷\frac {8}{5}=$ $\frac {8}{9}-\frac {2}{3}=$ $\frac {4}{5}÷\frac {3}{50}=$
$\frac {7}{20}÷14=$ $\frac {9}{10}-\frac {5}{8}=$ $\frac {5}{6}×\frac {2}{3}=$

一、$\frac {3}{5}$ $\frac {21}{2}$ 9
$\frac {5}{18}$ $\frac {1}{4}$ $\frac {4}{5}$
$\frac {17}{6}$ $\frac {3}{20}$ $\frac {33}{40}$
3 $\frac {14}{25}$ $\frac {1}{21}$
$\frac {4}{3}$ $\frac {7}{10}$ $\frac {25}{24}$
$\frac {1}{6}$ $\frac {2}{9}$ $\frac {40}{3}$
$\frac {1}{40}$ $\frac {11}{40}$ $\frac {5}{9}$

二、解方程。
$\frac {3}{16}x= \frac {3}{8}$ $25x= \frac {50}{7}$ $\frac {6}{7}x= 42$
$\frac {1}{7}+x= \frac {1}{3}$ $\frac {8}{9}x= \frac {16}{27}$ $x+\frac {11}{25}= \frac {4}{5}$

二、$x=2$
$x=\frac {2}{7}$
$x=49$
$x=\frac {4}{21}$
$x=\frac {2}{3}$
$x=\frac {9}{25}$