一、口算。
$\frac{2}{3} ÷ 4 =$
$1.4 × \frac{7}{10} =$
$\frac{1}{2} ÷ \frac{2}{3} =$
$\frac{17}{15} × 60 =$
$\frac{3}{14} × \frac{7}{12} =$
$\frac{7}{9} - \frac{4}{15} =$
$\frac{15}{16} ÷ \frac{2}{3} =$
$\frac{5}{7} ÷ \frac{9}{14} =$
$6 - \frac{3}{4} =$
$\frac{3}{5} ÷ \frac{5}{6} =$
$\frac{5}{4} × \frac{12}{5} =$
$\frac{2}{7} + \frac{2}{3} =$
$18 ÷ \frac{2}{11} =$
$\frac{21}{4} × \frac{4}{7} =$
$\frac{9}{5} ÷ \frac{3}{5} =$
$\frac{2}{7} × \frac{2}{3} =$
$\frac{7}{10} × \frac{5}{6} =$
$\frac{5}{6} ÷ \frac{7}{8} =$
$\frac{8}{9} ÷ \frac{4}{7} =$
$\frac{2}{9} + \frac{1}{6} =$
$\frac{5}{6} ÷ \frac{2}{3} =$

1.$\frac{1}{6}$ 2.$\frac{49}{50}$ 3.$\frac{3}{4}$ 4.$68$ 5.$\frac{1}{8}$ 6.$\frac{23}{45}$ 7.$\frac{45}{32}$ 8.$\frac{10}{9}$ 9.$5\frac{1}{4}$ 10.$\frac{18}{25}$ 11.$3$ 12.$\frac{20}{21}$ 13.$99$ 14.$3$ 15.$3$ 16.$\frac{4}{21}$ 17.$\frac{7}{12}$ 18.$\frac{20}{21}$ 19.$\frac{14}{9}$ 20.$\frac{7}{18}$ 21.$\frac{5}{4}$

二、计算下面各题，能用简便算法的就用简便算法。
$91 - 91×\frac{4}{13}$
$1 - \frac{5}{8}÷\frac{25}{28} - \frac{3}{10}$
$(\frac{1}{4} + \frac{1}{3})÷(\frac{1}{2} - \frac{1}{3})$
$(\frac{7}{11} - \frac{3}{8})×88$
$\frac{5}{16}÷[\frac{5}{7} - (\frac{1}{2} - \frac{2}{7})]$
$\frac{11}{12}÷(\frac{1}{9} + \frac{5}{12})×\frac{9}{11}$

1.$63$ 2.$0$ 3.$\frac{7}{2}$ 4.$23$ 5.$\frac{5}{8}$ 6.$\frac{27}{19}$