一、口算。
$\frac{9}{10}×\frac{2}{3}=$ $\frac{3}{8}×\frac{8}{5}=$ $20×\frac{5}{16}=$
$0.25×\frac{1}{5}=$ $\frac{1}{8}×\frac{6}{7}=$ $\frac{2}{5}×\frac{3}{4}=$
$\frac{5}{22}×2=$ $1.4×\frac{1}{2}=$ $0.8×\frac{3}{7}=$
$\frac{2}{3}×1.5=$ $\frac{3}{16}×0.8=$ $\frac{3}{4}×\frac{8}{27}=$
$\frac{9}{10}×15=$ $\frac{6}{7}×\frac{3}{2}=$ $\frac{11}{18}×\frac{9}{5}=$
$\frac{9}{8}×\frac{3}{4}=$ $\frac{5}{6}×\frac{2}{9}=$ $\frac{5}{8}×\frac{16}{15}=$
$\frac{3}{5}×0.25=$ $\frac{5}{7}×\frac{7}{10}=$ $\frac{5}{4}×\frac{2}{3}=$

1.$\frac{3}{5}$ 2.$\frac{3}{5}$ 3.$\frac{25}{4}$ 4.$\frac{1}{20}$ 5.$\frac{3}{28}$ 6.$\frac{3}{10}$ 7.$\frac{5}{11}$ 8.$\frac{7}{10}$ 9.$\frac{12}{35}$ 10.$1$ 11.$\frac{3}{20}$ 12.$\frac{2}{9}$ 13.$\frac{27}{2}$ 14.$\frac{9}{7}$ 15.$\frac{11}{10}$ 16.$\frac{27}{32}$ 17.$\frac{5}{27}$ 18.$\frac{2}{3}$ 19.$\frac{3}{20}$ 20.$\frac{1}{2}$ 21.$\frac{5}{6}$

二、计算下面各题，能用简便算法的就用简便算法。
$\frac{7}{8} + \frac{1}{2} × \frac{5}{6}$
$\frac{8}{9} - \frac{8}{9} × \frac{4}{5} + \frac{1}{5}$
$\frac{7}{13} × \frac{5}{2} × \frac{26}{35}$
$30 × ( \frac{1}{5} + \frac{1}{6} )$
$\frac{3}{8} + \frac{3}{8} × \frac{4}{7} + \frac{3}{8} × \frac{3}{7}$
$\frac{7}{10} × \frac{52}{5} - \frac{7}{10} × \frac{2}{5}$

1.$\frac{31}{24}$ 2.$\frac{17}{45}$ 3.$1$ 4.$11$ 5.$\frac{3}{4}$ 6.$7$