一、口算。
$\frac {3}{10}×\frac {5}{9}=$
$\frac {2}{3}+\frac {3}{4}=$
$2÷\frac {3}{4}=$
$\frac {5}{14}÷\frac {5}{8}=$
$\frac {1}{5}÷3=$
$\frac {3}{4}+\frac {1}{2}=$
$\frac {1}{2}-\frac {1}{14}=$
$\frac {5}{8}-\frac {1}{3}=$
$\frac {3}{7}÷\frac {8}{21}=$
$16×\frac {7}{8}=$
$\frac {5}{18}÷10=$
$\frac {7}{24}×\frac {9}{14}=$
$\frac {3}{7}÷\frac {5}{7}=$
$\frac {7}{15}×20=$
$\frac {7}{6}-\frac {5}{8}=$
$\frac {3}{4}÷\frac {1}{2}=$
$\frac {1}{2}+\frac {1}{5}=$
$\frac {4}{5}×\frac {1}{4}=$
$4-\frac {7}{18}=$
$10÷\frac {4}{5}=$
$\frac {1}{12}+\frac {5}{48}=$

1. $\frac{3}{10}×\frac{5}{9}=\frac{1}{6}$
2. $\frac{2}{3}+\frac{3}{4}=\frac{8 + 9}{12}=\frac{17}{12}$
3. $2÷\frac{3}{4}=2×\frac{4}{3}=\frac{8}{3}$
4. $\frac{5}{14}÷\frac{5}{8}=\frac{5}{14}×\frac{8}{5}=\frac{4}{7}$
5. $\frac{1}{5}÷3=\frac{1}{5}×\frac{1}{3}=\frac{1}{15}$
6. $\frac{3}{4}+\frac{1}{2}=\frac{3 + 2}{4}=\frac{5}{4}$
7. $\frac{1}{2}-\frac{1}{14}=\frac{7 - 1}{14}=\frac{3}{7}$
8. $\frac{5}{8}-\frac{1}{3}=\frac{15 - 8}{24}=\frac{7}{24}$
9. $\frac{3}{7}÷\frac{8}{21}=\frac{3}{7}×\frac{21}{8}=\frac{9}{8}$
10. $16×\frac{7}{8}=14$
11. $\frac{5}{18}÷10=\frac{5}{18}×\frac{1}{10}=\frac{1}{36}$
12. $\frac{7}{24}×\frac{9}{14}=\frac{3}{16}$
13. $\frac{3}{7}÷\frac{5}{7}=\frac{3}{7}×\frac{7}{5}=\frac{3}{5}$
14. $\frac{7}{15}×20=\frac{28}{3}$
15. $\frac{7}{6}-\frac{5}{8}=\frac{28 - 15}{24}=\frac{13}{24}$
16. $\frac{3}{4}÷\frac{1}{2}=\frac{3}{4}×2=\frac{3}{2}$
17. $\frac{1}{2}+\frac{1}{5}=\frac{5 + 2}{10}=\frac{7}{10}$
18. $\frac{4}{5}×\frac{1}{4}=\frac{1}{5}$
19. $4-\frac{7}{18}=\frac{72 - 7}{18}=\frac{65}{18}$
20. $10÷\frac{4}{5}=10×\frac{5}{4}=\frac{25}{2}$
21. $\frac{1}{12}+\frac{5}{48}=\frac{4 + 5}{48}=\frac{3}{16}$

二、解方程。
$\frac {3}{4}x-\frac {1}{5}x= \frac {11}{12}$
$12x+3.6= 8.4$
$x-0.25x= 3$
$\frac {1}{2}x÷\frac {2}{3}= \frac {3}{2}$
$\frac {5}{8}x-\frac {1}{8}= \frac {3}{4}$
$5(x+36)= 560$

二、$x=\frac{5}{3}$ $x=0.4$ $x=4$ $x=2$ $x=\frac{7}{5}$ $x=76$

解：$\frac{3}{4}x - \frac{1}{5}x = \frac{11}{12}$
$\frac{15}{20}x - \frac{4}{20}x = \frac{11}{12}$
$\frac{11}{20}x = \frac{11}{12}$
$x = \frac{11}{12} ÷ \frac{11}{20}$
$x = \frac{5}{3}$
解：$12x + 3.6 = 8.4$
$12x = 8.4 - 3.6$
$12x = 4.8$
$x = 4.8 ÷ 12$
$x = 0.4$
解：$x - 0.25x = 3$
$0.75x = 3$
$x = 3 ÷ 0.75$
$x = 4$
解：$\frac{1}{2}x ÷ \frac{2}{3} = \frac{3}{2}$
$\frac{1}{2}x = \frac{3}{2} × \frac{2}{3}$
$\frac{1}{2}x = 1$
$x = 1 × 2$
$x = 2$
解：$\frac{5}{8}x - \frac{1}{8} = \frac{3}{4}$
$\frac{5}{8}x = \frac{3}{4} + \frac{1}{8}$
$\frac{5}{8}x = \frac{7}{8}$
$x = \frac{7}{8} ÷ \frac{5}{8}$
$x = \frac{7}{5}$
解：$5(x + 36) = 560$
$x + 36 = 560 ÷ 5$
$x + 36 = 112$
$x = 112 - 36$
$x = 76$