一、口算。
$\frac{7}{10} ÷ \frac{21}{40} =$
$25\% × 4 =$
$7 - \frac{5}{9} - \frac{4}{9} =$
$\frac{5}{8} ÷ \frac{2}{3} =$
$\frac{2}{21} × \frac{7}{8} =$
$( \frac{4}{5} + \frac{1}{7} ) × 35 =$
$16 × 50\% =$
$4 ÷ 48\% =$
$\frac{2}{19} + \frac{17}{19} ÷ \frac{17}{18} =$
$\frac{4}{5} × \frac{1}{8} =$
$16 ÷ \frac{4}{5} =$
$\frac{1}{4} × 4 ÷ \frac{1}{4} × 4 =$
$\frac{9}{14} - \frac{3}{7} =$
$\frac{8}{7} × 0.8 =$
$1.7 - 0.25 - 75\% =$
$\frac{4}{7} ÷ \frac{16}{21} =$
$\frac{3}{5} ÷ \frac{1}{10} =$
$\frac{1}{4} ÷ 25\% × \frac{1}{8} =$
$40\% × \frac{5}{6} =$
$10 ÷ 2\% =$
$( \frac{8}{9} - \frac{2}{3} ) × \frac{3}{4} =$

1.$\frac{4}{3}$ 2.$1$ 3.$6$ 4.$\frac{15}{16}$ 5.$\frac{1}{12}$ 6.$33$ 7.$8$ 8.$\frac{25}{3}$ 9.$\frac{20}{19}$ 10.$\frac{1}{10}$ 11.$20$ 12.$16$ 13.$\frac{3}{14}$ 14.$\frac{32}{35}$ 15.$0.7$ 16.$\frac{3}{4}$ 17.$6$ 18.$\frac{1}{8}$ 19.$\frac{1}{3}$ 20.$500$ 21.$\frac{1}{6}$

二、计算下面各题，能用简便算法的就用简便算法。
$\frac{1}{6} ÷ [1 ÷ (\frac{3}{5} - \frac{3}{10})]$
$4.8 × 96 + 4.8 ÷ \frac{1}{4}$
$41 × 25\% - 0.25 + \frac{1}{4} × 60$
$\frac{13}{11} - \frac{3}{7} ÷ \frac{3}{5} - \frac{2}{7}$
$2.5 × (\frac{2}{5} - \frac{1}{3})$
$\frac{3}{4} × [(100\% - \frac{1}{5}) × 25\%]$

1.$\frac{1}{20}$ 2.$480$ 3.$25$ 4.$\frac{2}{11}$ 5.$\frac{1}{6}$ 6.$\frac{3}{20}$