一、口算。
$\frac {3}{4}-\frac {1}{20}=$
$\frac {8}{3}÷\frac {8}{5}=$
$\frac {7}{2}×\frac {2}{5}=$
$\frac {3}{2}×\frac {2}{3}=$
$\frac {7}{20}×\frac {5}{14}=$
$\frac {2}{15}+\frac {1}{5}=$
$\frac {5}{9}÷\frac {20}{3}=$
$\frac {8}{25}÷\frac {4}{5}=$
$\frac {2}{5}-\frac {2}{7}=$
$\frac {11}{12}-\frac {5}{8}=$
$\frac {12}{5}×\frac {1}{6}=$
$\frac {1}{8}÷\frac {1}{4}=$
$\frac {5}{12}×\frac {9}{10}=$
$\frac {3}{16}+\frac {1}{12}=$
$\frac {3}{8}×\frac {1}{6}=$
$\frac {5}{12}÷\frac {1}{4}=$
$\frac {4}{5}×\frac {7}{12}=$
$\frac {32}{11}÷\frac {2}{33}=$
$\frac {2}{3}+\frac {7}{20}=$
$\frac {3}{5}÷\frac {3}{10}=$
$\frac {8}{9}×\frac {3}{8}=$

一、$\frac {7}{10}$ $\frac {5}{3}$ $\frac {7}{5}$ 1 $\frac {1}{8}$ $\frac {1}{3}$ $\frac {1}{12}$ $\frac {2}{5}$ $\frac {4}{35}$ $\frac {7}{24}$ $\frac {2}{5}$ $\frac {1}{2}$ $\frac {3}{8}$ $\frac {13}{48}$ $\frac {1}{16}$ $\frac {5}{3}$ $\frac {7}{15}$ 48 $\frac {61}{60}$ 2 $\frac {1}{3}$

$\frac{3}{4} - \frac{1}{20} = \frac{15}{20} - \frac{1}{20} = \frac{14}{20} = \frac{7}{10}$
$\frac{8}{3} ÷ \frac{8}{5} = \frac{8}{3} × \frac{5}{8} = \frac{5}{3}$
$\frac{7}{2} × \frac{2}{5} = \frac{14}{10} = \frac{7}{5}$
$\frac{3}{2} × \frac{2}{3} = 1$
$\frac{7}{20} × \frac{5}{14} = \frac{35}{280} = \frac{1}{8}$
$\frac{2}{15} + \frac{1}{5} = \frac{2}{15} + \frac{3}{15} = \frac{5}{15} = \frac{1}{3}$
$\frac{5}{9} ÷ \frac{20}{3} = \frac{5}{9} × \frac{3}{20} = \frac{15}{180} = \frac{1}{12}$
$\frac{8}{25} ÷ \frac{4}{5} = \frac{8}{25} × \frac{5}{4} = \frac{40}{100} = \frac{2}{5}$
$\frac{2}{5} - \frac{2}{7} = \frac{14}{35} - \frac{10}{35} = \frac{4}{35}$
$\frac{11}{12} - \frac{5}{8} = \frac{22}{24} - \frac{15}{24} = \frac{7}{24}$
$\frac{12}{5} × \frac{1}{6} = \frac{12}{30} = \frac{2}{5}$
$\frac{1}{8} ÷ \frac{1}{4} = \frac{1}{8} × 4 = \frac{4}{8} = \frac{1}{2}$
$\frac{5}{12} × \frac{9}{10} = \frac{45}{120} = \frac{3}{8}$
$\frac{3}{16} + \frac{1}{12} = \frac{9}{48} + \frac{4}{48} = \frac{13}{48}$
$\frac{3}{8} × \frac{1}{6} = \frac{3}{48} = \frac{1}{16}$
$\frac{5}{12} ÷ \frac{1}{4} = \frac{5}{12} × 4 = \frac{20}{12} = \frac{5}{3}$
$\frac{4}{5} × \frac{7}{12} = \frac{28}{60} = \frac{7}{15}$
$\frac{32}{11} ÷ \frac{2}{33} = \frac{32}{11} × \frac{33}{2} = \frac{1056}{22} = 48$
$\frac{2}{3} + \frac{7}{20} = \frac{40}{60} + \frac{21}{60} = \frac{61}{60}$
$\frac{3}{5} ÷ \frac{3}{10} = \frac{3}{5} × \frac{10}{3} = 2$
$\frac{8}{9} × \frac{3}{8} = \frac{24}{72} = \frac{1}{3}$

二、简便计算下面各题。
$35÷\frac {7}{8}-\frac {2}{7}-\frac {5}{7}$
$(54+\frac {9}{13})÷9+\frac {12}{13}$
$\frac {5}{9}×\frac {3}{4}+\frac {5}{9}×\frac {1}{4}$
$(\frac {5}{8}-\frac {5}{8}×\frac {4}{5})÷\frac {5}{2}$
$(\frac {5}{6}+\frac {7}{8}-\frac {5}{12})÷\frac {1}{24}$
$\frac {9}{19}÷[\frac {1}{3}×(\frac {4}{19}+\frac {5}{19})]$

二、39 7 $\frac {5}{9}$ $\frac {1}{20}$ 31 3

$35÷\frac {7}{8}-\frac {2}{7}-\frac {5}{7}$
$=35×\frac {8}{7}-(\frac {2}{7}+\frac {5}{7})$
$=40 - 1$
$=39$
$(54+\frac {9}{13})÷9+\frac {12}{13}$
$=54×\frac {1}{9}+\frac {9}{13}×\frac {1}{9}+\frac {12}{13}$
$=6 + \frac {1}{13}+\frac {12}{13}$
$=6 + 1$
$=7$
$\frac {5}{9}×\frac {3}{4}+\frac {5}{9}×\frac {1}{4}$
$=\frac {5}{9}×(\frac {3}{4}+\frac {1}{4})$
$=\frac {5}{9}×1$
$=\frac {5}{9}$
$(\frac {5}{8}-\frac {5}{8}×\frac {4}{5})÷\frac {5}{2}$
$=(\frac {5}{8}-\frac {4}{8})×\frac {2}{5}$
$=\frac {1}{8}×\frac {2}{5}$
$=\frac {1}{20}$
$(\frac {5}{6}+\frac {7}{8}-\frac {5}{12})÷\frac {1}{24}$
$=\frac {5}{6}×24+\frac {7}{8}×24-\frac {5}{12}×24$
$=20 + 21 - 10$
$=31$
$\frac {9}{19}÷[\frac {1}{3}×(\frac {4}{19}+\frac {5}{19})]$
$=\frac {9}{19}÷[\frac {1}{3}×\frac {9}{19}]$
$=\frac {9}{19}÷\frac {3}{19}$
$=\frac {9}{19}×\frac {19}{3}$
$=3$