一、直接写出得数。
$\frac {3}{7} + \frac {1}{7} + \frac {5}{7} =$
$\frac {3}{4} - \frac {5}{7} + \frac {1}{4} =$
$\frac {5}{6} - \frac {2}{3} =$

1. $\frac{9}{7}$ 2. $\frac{3}{5}$ 3. $\frac{2}{7}$ 4. $9\frac{1}{2}$ 5. $\frac{1}{6}$ 6. $1\frac{1}{10}$

二、计算下面各题。
$\frac {5}{6} - \frac {1}{4} + \frac {1}{3}$ $\frac {1}{5} + \frac {7}{1 5} + \frac {4}{1 5}$
$\frac {7}{1 0} - (\frac {3}{4} - \frac {2}{5})$ $\frac {1 3}{1 5} - (\frac {1}{3} + \frac {2}{5})$

1. $\frac{11}{12}$ 2. $\frac{14}{15}$ 3. $\frac{7}{20}$ 4. $\frac{2}{15}$