三、算一算。
1. 直接写出得数。
$\frac{1}{5} + \frac{1}{7} =$
$\frac{7}{9} - \frac{1}{9} =$
$0.95 - \frac{3}{5} =$
$\frac{3}{4} - \frac{4}{7} =$
$2 - \frac{5}{14} =$
$1 - \frac{11}{23} - \frac{12}{23} =$
$\frac{1}{3} - \frac{1}{8} =$
$\frac{1}{3} + \frac{8}{9} - \frac{1}{3} =$

$\frac{1}{5} + \frac{1}{7} = \frac{12}{35}$
$\frac{7}{9} - \frac{1}{9} = \frac{2}{3}$
$0.95 - \frac{3}{5} = 0.35$
$\frac{3}{4} - \frac{4}{7} = \frac{5}{28}$
$2 - \frac{5}{14} = 1\frac{9}{14}$
$1 - \frac{11}{23} - \frac{12}{23} = 0$
$\frac{1}{3} - \frac{1}{8} = \frac{5}{24}$
$\frac{1}{3} + \frac{8}{9} - \frac{1}{3} = \frac{8}{9}$

2. 计算下面各题,能简算的要简算。
$5 - \frac{3}{7} - \frac{4}{7}$
$\frac{1}{6} + \frac{3}{8} + \frac{5}{8}$
$\frac{5}{9} - (\frac{5}{6} - \frac{7}{12})$

$5 - \frac{3}{7} - \frac{4}{7}$
$= 5 - (\frac{3}{7} + \frac{4}{7})$
$= 5 - 1$
$= 4$
$\frac{1}{6} + \frac{3}{8} + \frac{5}{8}$
$= \frac{1}{6} + (\frac{3}{8} + \frac{5}{8})$
$= \frac{1}{6} + 1$
$= 1\frac{1}{6}$
$\frac{5}{9} - (\frac{5}{6} - \frac{7}{12})$
$= \frac{5}{9} - (\frac{10}{12} - \frac{7}{12})$
$= \frac{5}{9} - \frac{1}{4}$
$= \frac{20}{36} - \frac{9}{36}$
$= \frac{11}{36}$

3. 解方程。
$\frac{1}{3} + x = \frac{5}{12}$
$x + \frac{1}{5} = \frac{8}{15}$
$x - (\frac{1}{4} + \frac{1}{5}) = \frac{11}{20}$

解：
$\frac{1}{3} + x = \frac{5}{12}$
$x = \frac{5}{12} - \frac{1}{3}$
$x = \frac{5}{12} - \frac{4}{12}$
$x = \frac{1}{12}$
$x + \frac{1}{5} = \frac{8}{15}$
$x = \frac{8}{15} - \frac{1}{5}$
$x = \frac{8}{15} - \frac{3}{15}$
$x = \frac{5}{15}$
$x = \frac{1}{3}$
$x - (\frac{1}{4} + \frac{1}{5}) = \frac{11}{20}$
$x - \frac{9}{20} = \frac{11}{20}$
$x = \frac{11}{20} + \frac{9}{20}$
$x = 1$

四、解决问题。
1. 王叔叔家来了几个客人，他沏了一壶四川特产名茶蒙顶甘露，第一次倒了这壶蒙顶甘露的$\frac{2}{7}$，第二次倒了这壶蒙顶甘露的$\frac{1}{3}$。两次一共倒了这壶蒙顶甘露的几分之几？还剩几分之几？

1. $\frac{2}{7} + \frac{1}{3} = \frac{13}{21}$
$1 - \frac{13}{21} = \frac{8}{21}$