一、口算。
$\frac{1}{5} - \frac{1}{8} =$ $\frac{2}{7} × \frac{5}{3} =$ $\frac{3}{4} × \frac{5}{6} × \frac{4}{5} =$
$\frac{16}{27} × \frac{3}{2} =$ $\frac{9}{31} × \frac{31}{90} =$ $\frac{2}{5} × 4 × \frac{3}{4} =$
$\frac{1}{2} × \frac{3}{5} =$ $\frac{8}{5} × \frac{35}{48} =$ $\frac{7}{8} × 47 × \frac{8}{7} =$
$\frac{11}{24} × \frac{8}{33} =$ $\frac{7}{5} × 1.5 =$ $28 × ( \frac{1}{4} - \frac{1}{7} ) =$
$\frac{5}{16} × \frac{4}{15} =$ $\frac{2}{3} × 7.2 =$ $\frac{3}{4} × 56 × \frac{3}{14} =$
$\frac{7}{18} × 1.2 =$ $\frac{3}{34} × 0.68 =$ $\frac{5}{24} × \frac{2}{9} × 24 =$
$\frac{12}{7} × 0.21 =$ $\frac{6}{17} × \frac{34}{3} =$ $\frac{11}{12} × \frac{9}{10} × \frac{10}{9} =$

1.$\frac{3}{40}$ 2.$\frac{10}{21}$ 3.$\frac{1}{2}$ 4.$\frac{8}{9}$ 5.$\frac{1}{10}$ 6.$\frac{6}{5}$ 7.$\frac{3}{10}$ 8.$\frac{7}{6}$ 9.$47$ 10.$\frac{1}{9}$ 11.$2.1$ 12.$3$ 13.$\frac{1}{12}$ 14.$4.8$ 15.$9$ 16.$\frac{7}{15}$ 17.$0.06$ 18.$\frac{10}{9}$ 19.$0.36$ 20.$4$ 21.$\frac{11}{12}$

二、计算下面各题。
$\frac{3}{10} × ( \frac{5}{7} - \frac{10}{21} ) + \frac{1}{2}$
$\frac{8}{9} × ( \frac{4}{5} - \frac{5}{6} × 0.6 )$
$\frac{1}{4} + ( \frac{3}{4} - \frac{1}{12} ) × \frac{3}{5}$
$\frac{1}{16} + \frac{1}{2} × \frac{5}{8} - \frac{1}{4}$
$\frac{24}{25} × ( \frac{2}{3} + \frac{5}{6} × \frac{3}{10} )$
$\frac{1}{5} + \frac{5}{3} × \frac{6}{7} × \frac{14}{25}$

1.$\frac{4}{7}$ 2.$\frac{4}{15}$ 3.$\frac{13}{20}$ 4.$\frac{1}{8}$ 5.$\frac{22}{25}$ 6.$1$