1. 直接写出得数。
$\frac{1}{3}+\frac{2}{3}=$
$\frac{4}{5}-\frac{1}{5}=$
$\frac{1}{6}+\frac{2}{6}=$
$\frac{1}{8}+\frac{3}{8}=$
$\frac{5}{11}-\frac{3}{11}=$
$\frac{3}{13}-\frac{1}{13}=$
$\frac{2}{3}-\frac{1}{3}=$
$\frac{3}{7}+\frac{4}{7}=$
$\frac{3}{7}-\frac{3}{7}=$
$\frac{2}{5}+\frac{2}{5}=$
$1-\frac{1}{6}=$
$\frac{2}{3}+0=$

1
$\frac{3}{5}$
$\frac{1}{2}$
$\frac{1}{2}$
$\frac{2}{11}$
$\frac{2}{13}$
$\frac{1}{3}$
1
0
$\frac{4}{5}$
$\frac{5}{6}$
$\frac{2}{3}$

2. 画一画，填一填。
$\frac{1}{3} + \frac{2}{9} = ( ) + ( ) = ( )$
$\frac{1}{3} - \frac{2}{9} = ( ) - ( ) = ( )$
$\frac{1}{2} - \frac{1}{4} = ( ) - ( ) = ( )$
$\frac{1}{2} + \frac{1}{4} = ( ) + ( ) = ( )$

$\frac{1}{3} + \frac{2}{9} = \frac{3}{9} + \frac{2}{9} = \frac{5}{9}$
$\frac{1}{3} - \frac{2}{9} = \frac{3}{9} - \frac{2}{9} = \frac{1}{9}$
$\frac{1}{2} - \frac{1}{4} = \frac{2}{4} - \frac{1}{4} = \frac{1}{4}$
$\frac{1}{2} + \frac{1}{4} = \frac{2}{4} + \frac{1}{4} = \frac{3}{4}$

3. 森林医生。

1/3 + 1/9 = 3/9 + 1/9 = 4/9
7/8 - 3/4 = 7/8 - 6/8 = 1/8