一、口算。
$\frac {4}{9}÷\frac {2}{3}=$
$\frac {2}{15}+\frac {1}{5}=$
$40×\frac {2}{5}=$
$1-\frac {3}{10}=$
$12×\frac {3}{8}=$
$\frac {4}{5}÷\frac {3}{5}=$
$\frac {8}{25}÷\frac {4}{5}=$
$\frac {1}{2}÷\frac {1}{4}=$
$\frac {5}{6}+\frac {3}{8}=$
$\frac {2}{3}÷\frac {4}{9}=$
$\frac {1}{8}×5=$
$\frac {5}{7}×\frac {2}{5}=$
$\frac {2}{3}-\frac {1}{5}=$
$\frac {2}{3}÷\frac {3}{5}=$
$\frac {7}{20}÷\frac {4}{15}=$
$\frac {5}{6}×\frac {3}{4}=$
$\frac {5}{6}÷\frac {5}{18}=$
$\frac {7}{15}-\frac {3}{10}=$
$\frac {6}{7}÷\frac {3}{14}=$
$\frac {2}{3}×\frac {2}{7}=$
$12÷\frac {3}{8}=$

1. $\frac{4}{9}÷\frac{2}{3}=\frac{4}{9}×\frac{3}{2}=\frac{2}{3}$
2. $\frac{2}{15}+\frac{1}{5}=\frac{2}{15}+\frac{3}{15}=\frac{1}{3}$
3. $40×\frac{2}{5}=16$
4. $1 - \frac{3}{10}=\frac{7}{10}$
5. $12×\frac{3}{8}=\frac{9}{2}$
6. $\frac{4}{5}÷\frac{3}{5}=\frac{4}{5}×\frac{5}{3}=\frac{4}{3}$
7. $\frac{8}{25}÷\frac{4}{5}=\frac{8}{25}×\frac{5}{4}=\frac{2}{5}$
8. $\frac{1}{2}÷\frac{1}{4}=\frac{1}{2}×4 = 2$
9. $\frac{5}{6}+\frac{3}{8}=\frac{20}{24}+\frac{9}{24}=\frac{29}{24}$
10. $\frac{2}{3}÷\frac{4}{9}=\frac{2}{3}×\frac{9}{4}=\frac{3}{2}$
11. $\frac{1}{8}×5=\frac{5}{8}$
12. $\frac{5}{7}×\frac{2}{5}=\frac{2}{7}$
13. $\frac{2}{3}-\frac{1}{5}=\frac{10}{15}-\frac{3}{15}=\frac{7}{15}$
14. $\frac{2}{3}÷\frac{3}{5}=\frac{2}{3}×\frac{5}{3}=\frac{10}{9}$
15. $\frac{7}{20}÷\frac{4}{15}=\frac{7}{20}×\frac{15}{4}=\frac{21}{16}$
16. $\frac{5}{6}×\frac{3}{4}=\frac{5}{8}$
17. $\frac{5}{6}÷\frac{5}{18}=\frac{5}{6}×\frac{18}{5}=3$
18. $\frac{7}{15}-\frac{3}{10}=\frac{14}{30}-\frac{9}{30}=\frac{1}{6}$
19. $\frac{6}{7}÷\frac{3}{14}=\frac{6}{7}×\frac{14}{3}=4$
20. $\frac{2}{3}×\frac{2}{7}=\frac{4}{21}$
21. $12÷\frac{3}{8}=12×\frac{8}{3}=32$
综上，答案依次为：$\frac{2}{3}$；$\frac{1}{3}$；$16$；$\frac{7}{10}$；$\frac{9}{2}$；$\frac{4}{3}$；$\frac{2}{5}$；$2$；$\frac{29}{24}$；$\frac{3}{2}$；$\frac{5}{8}$；$\frac{2}{7}$；$\frac{7}{15}$；$\frac{10}{9}$；$\frac{21}{16}$；$\frac{5}{8}$；$3$；$\frac{1}{6}$；$4$；$\frac{4}{21}$；$32$。

二、计算下面各题,怎样简便就怎样计算。
$\frac {4}{7}×\frac {12}{19}+\frac {4}{7}×\frac {7}{19}$
$\frac {1}{10}÷(\frac {7}{5}-\frac {2}{7}×\frac {21}{5})$
$\frac {4}{15}÷\frac {8}{35}×(\frac {9}{14}-\frac {4}{7})$
$4-\frac {5}{11}-\frac {6}{11}$
$[1-(\frac {3}{4}-\frac {3}{8})]÷\frac {5}{6}$
$14÷[(\frac {8}{9}-\frac {2}{3})×\frac {9}{2}]$

二、$\frac{4}{7}$ $\frac{1}{2}$ $\frac{1}{12}$ 3 $\frac{3}{4}$ 14

1. $\frac{4}{7}×\frac{12}{19}+\frac{4}{7}×\frac{7}{19}$
解：$=\frac{4}{7}×(\frac{12}{19}+\frac{7}{19})$
$=\frac{4}{7}×1$
$=\frac{4}{7}$
2. $\frac{1}{10}÷(\frac{7}{5}-\frac{2}{7}×\frac{21}{5})$
解：$=\frac{1}{10}÷(\frac{7}{5}-\frac{6}{5})$
$=\frac{1}{10}÷\frac{1}{5}$
$=\frac{1}{10}×5$
$=\frac{1}{2}$
3. $\frac{4}{15}÷\frac{8}{35}×(\frac{9}{14}-\frac{4}{7})$
解：$=\frac{4}{15}×\frac{35}{8}×(\frac{9}{14}-\frac{8}{14})$
$=\frac{7}{6}×\frac{1}{14}$
$=\frac{1}{12}$
4. $4-\frac{5}{11}-\frac{6}{11}$
解：$=4-(\frac{5}{11}+\frac{6}{11})$
$=4-1$
$=3$
5. $[1-(\frac{3}{4}-\frac{3}{8})]÷\frac{5}{6}$
解：$=[1-(\frac{6}{8}-\frac{3}{8})]×\frac{6}{5}$
$=(1-\frac{3}{8})×\frac{6}{5}$
$=\frac{5}{8}×\frac{6}{5}$
$=\frac{3}{4}$
6. $14÷[(\frac{8}{9}-\frac{2}{3})×\frac{9}{2}]$
解：$=14÷[(\frac{8}{9}-\frac{6}{9})×\frac{9}{2}]$
$=14÷(\frac{2}{9}×\frac{9}{2})$
$=14÷1$
$=14$