一、口算。
$\frac{2}{5}×\frac{7}{8}=$
$6.4×\frac{1}{4}=$
$\frac{7}{9}×\frac{9}{14}=$
$\frac{2}{3}-\frac{5}{12}=$
$\frac{3}{4}×\frac{1}{3}=$
$0.8×\frac{5}{4}=$
$\frac{2}{7}×0.21=$
$\frac{3}{5}×10=$
$\frac{2}{5}×\frac{2}{5}=$
$\frac{5}{28}×\frac{7}{10}=$
$\frac{9}{10}×\frac{25}{27}=$
$44×\frac{5}{44}=$
$\frac{5}{6}×\frac{1}{5}=$
$\frac{6}{7}×\frac{5}{9}=$
$\frac{5}{8}×1.4=$
$\frac{4}{7}×0.125=$
$\frac{3}{4}-\frac{1}{6}=$
$\frac{2}{5}+\frac{1}{2}=$
$\frac{2}{3}×\frac{6}{7}=$
$\frac{20}{3}×\frac{9}{10}=$
$\frac{4}{9}×\frac{1}{3}=$

1.$\frac{7}{20}$ 2.$1.6$ 3.$\frac{1}{2}$ 4.$\frac{1}{4}$ 5.$\frac{1}{4}$ 6.$1$ 7.$0.06$ 8.$6$ 9.$\frac{4}{25}$ 10.$\frac{1}{8}$ 11.$\frac{5}{6}$ 12.$5$ 13.$\frac{1}{6}$ 14.$\frac{10}{21}$ 15.$\frac{7}{8}$ 16.$\frac{1}{14}$ 17.$\frac{7}{12}$ 18.$\frac{9}{10}$ 19.$\frac{4}{7}$ 20.$6$ 21.$\frac{4}{27}$

二、计算下面各题，能用简便算法的就用简便算法。
$87×\frac{5}{86}$
$14×\frac{6}{13}×\frac{2}{7}$
$\frac{5}{9}×0.75+\frac{5}{9}×0.25$
$\frac{13}{25}×199+\frac{13}{25}$
$\frac{5}{7}×\frac{7}{5}-\frac{5}{7}+\frac{3}{8}$
$\frac{4}{17}×23+\frac{11}{17}×4$

1.$5\frac{5}{86}$ 2.$\frac{24}{13}$ 3.$\frac{5}{9}$ 4.$104$ 5.$\frac{37}{56}$ 6.$8$