1. 直接写出得数。
$\frac{5}{16}×20=$ $\frac{7}{10}×100=$ $\frac{199}{200}×0=$ $\frac{5}{8}×16×\frac{2}{5}=$
$\frac{7}{10}×\frac{3}{14}=$ $\frac{5}{6}×\frac{10}{9}=$ $\frac{17}{30}×\frac{29}{17}=$ $\frac{4}{9}×\frac{2}{27}×27=$
$\frac{5}{12}×\frac{2}{7}=$ $\frac{16}{7}×\frac{7}{64}=$ $\frac{2}{15}×\frac{45}{8}=$ $\frac{7}{36}×\frac{4}{7}×\frac{14}{9}=$
$\frac{7}{11}×\frac{9}{14}=$ $\frac{5}{14}×\frac{7}{10}=$ $\frac{8}{21}×\frac{7}{12}=$ $\frac{5}{8}×\frac{1}{2}×\frac{2}{5}=$
$\frac{4}{9}×\frac{6}{5}=$ $\frac{1}{5}×\frac{12}{5}=$ $\frac{20}{21}×\frac{15}{16}=$ $\frac{3}{4}×\frac{2}{5}×\frac{7}{5}=$

1. $\frac{25}{4}$ 70 0 4 $\frac{3}{20}$ $\frac{25}{27}$ $\frac{29}{30}$ $\frac{8}{9}$ $\frac{5}{42}$ $\frac{1}{4}$ $\frac{3}{4}$ $\frac{14}{81}$ $\frac{9}{22}$ $\frac{1}{4}$ $\frac{2}{9}$ $\frac{1}{8}$ $\frac{8}{15}$ $\frac{12}{25}$ $\frac{25}{28}$ $\frac{21}{50}$

2. 计算下面各题。
$\frac{7}{15}×5×\frac{4}{21}$ $\frac{8}{15}×12×\frac{7}{16}$ $\frac{16}{39}×\frac{26}{27}×\frac{9}{10}$
$\frac{5}{7}×\frac{14}{15}×\frac{4}{21}$ $\frac{2}{9}×\frac{3}{20}×\frac{9}{11}$ $91×\frac{7}{13}×\frac{5}{49}$

2. $\frac{4}{9}$ $\frac{14}{5}$ $\frac{16}{45}$ $\frac{8}{63}$ $\frac{3}{110}$ 5

计算：$\frac{1×2 + 2×4 + 3×6 + 4×8}{2×3 + 4×6 + 6×9 + 8×12}$。

思维提升
$\frac{1}{3}$