1. 直接写得数。
$\frac{7}{8} - \frac{1}{4} = $
$\frac{1}{3} + \frac{2}{5} = $
$3 × \frac{3}{5} = $
$\frac{5}{8} × \frac{2}{5} = $
$\frac{2}{3} + \frac{3}{4} = $
$\frac{2}{3} × 18 = $
$\frac{7}{8} × \frac{4}{21} = $
$\frac{4}{7} × \frac{7}{4} = $
$\frac{1}{5} + \frac{1}{10} = $
$\frac{7}{8} + (\frac{1}{2} + \frac{1}{8}) = $

$\frac{5}{8}$
$\frac{11}{15}$
$\frac {9}{5}$
$\frac{1}{4}$
$\frac {17}{12}$
12
$\frac{1}{6}$
1
$\frac{3}{10}$
$\frac 32$

2. 下列各题怎样算简便就怎样算。
$\frac{7}{9} × \frac{2}{5} × \frac{9}{7} = $
$\frac{3}{5} × \frac{1}{2} × 15 = $
$\frac{11}{6} - \frac{3}{7} - \frac{4}{7} = $
$\frac{17}{18} - (\frac{1}{2} - \frac{1}{18}) = $

$=\frac 79×\frac 97×\frac 25$
$ =1×\frac 25$
$ =\frac 25$
$=\frac 35×15×\frac 12$
$ =9×\frac 12$
$ =\frac 92$
$=\frac {11}6-(\frac 37+\frac 47)$
$ =\frac {11}6-1$
$ =\frac 56$
$=\frac {17}{18}+\frac 1{18}-\frac 12$
$ =1-\frac 12$
$ =\frac 12$