一、口算。
$0.5×\frac {4}{17}=$
$\frac {1}{12}+\frac {8}{9}=$
$\frac {4}{5}×\frac {15}{16}=$
$80×\frac {1}{16}=$
$\frac {3}{2}-\frac {5}{6}=$
$\frac {5}{8}+\frac {9}{20}=$
$\frac {7}{12}×\frac {3}{14}=$
$\frac {1}{4}×\frac {2}{5}=$
$\frac {4}{11}×\frac {11}{12}=$
$24×\frac {7}{8}=$
$\frac {6}{7}-\frac {1}{4}=$
$\frac {1}{9}×\frac {3}{5}=$
$\frac {13}{9}×\frac {9}{5}=$
$\frac {1}{8}×\frac {2}{7}=$
$\frac {9}{10}×\frac {5}{6}=$
$\frac {3}{2}×\frac {2}{5}=$
$\frac {4}{7}×\frac {2}{3}=$
$\frac {5}{12}×15=$
$2-\frac {1}{9}=$
$\frac {6}{7}×\frac {2}{3}=$
$\frac {4}{9}+\frac {1}{4}=$

$\frac{2}{17}$ $\frac{35}{36}$ $\frac{3}{4}$ 5 $\frac{2}{3}$ $\frac{43}{40}$ $\frac{1}{8}$ $\frac{1}{10}$ $\frac{1}{3}$ 21 $\frac{17}{28}$ $\frac{1}{15}$ $\frac{13}{5}$ $\frac{1}{28}$ $\frac{3}{4}$ $\frac{3}{5}$ $\frac{8}{21}$ $\frac{25}{4}$ $\frac{17}{9}$ $\frac{4}{7}$ $\frac{25}{36}$

二、计算下面各题。
$\frac {40}{13}×26×\frac {7}{80}$
$72×\frac {1}{8}×\frac {1}{3}$
$\frac {9}{10}×\frac {2}{3}×\frac {5}{6}$
$\frac {17}{24}×\frac {3}{2}×\frac {2}{17}$
$\frac {8}{7}×\frac {5}{12}×42$
$\frac {19}{20}×\frac {4}{9}×\frac {25}{38}$

7 3 $\frac{1}{2}$ $\frac{1}{8}$ 20 $\frac{5}{18}$

$\frac{40}{13}×26×\frac{7}{80}$
$=\frac{40}{13}×26×\frac{7}{80}$
$=40×2×\frac{7}{80}$
$=80×\frac{7}{80}$
$=7$
$72×\frac{1}{8}×\frac{1}{3}$
$=9×\frac{1}{3}$
$=3$
$\frac{9}{10}×\frac{2}{3}×\frac{5}{6}$
$=\frac{3}{5}×\frac{5}{6}$
$=\frac{1}{2}$
$\frac{17}{24}×\frac{3}{2}×\frac{2}{17}$
$=\frac{17}{24}×\frac{3}{17}$
$=\frac{3}{24}$
$=\frac{1}{8}$
$\frac{8}{7}×\frac{5}{12}×42$
$=\frac{8}{7}×42×\frac{5}{12}$
$=48×\frac{5}{12}$
$=20$
$\frac{19}{20}×\frac{4}{9}×\frac{25}{38}$
$=\frac{19}{20}×\frac{25}{38}×\frac{4}{9}$
$=\frac{5}{8}×\frac{4}{9}$
$=\frac{5}{18}$
答案依次为：7；3；$\frac{1}{2}$；$\frac{1}{8}$；20；$\frac{5}{18}$