1. 算一算。
$\frac{5}{9}+\frac{1}{3}$ $1-\frac{3}{11}$ $\frac{2}{9}+\frac{1}{6}$ $\frac{1}{3}-\frac{1}{5}$
$\frac{7}{12}-\frac{3}{8}$ $\frac{5}{6}+\frac{1}{4}$ $\frac{1}{5}+\frac{1}{8}$ $\frac{4}{7}-\frac{1}{3}$

$\frac{5}{9}+\frac{1}{3}=\frac{5}{9}+\frac{3}{9}=\frac{8}{9}$
$1-\frac{3}{11}=\frac{11}{11}-\frac{3}{11}=\frac{8}{11}$
$\frac{2}{9}+\frac{1}{6}=\frac{4}{18}+\frac{3}{18}=\frac{7}{18}$
$\frac{1}{3}-\frac{1}{5}=\frac{5}{15}-\frac{3}{15}=\frac{2}{15}$
$\frac{7}{12}-\frac{3}{8}=\frac{14}{24}-\frac{9}{24}=\frac{5}{24}$
$\frac{5}{6}+\frac{1}{4}=\frac{10}{12}+\frac{3}{12}=\frac{13}{12}$
$\frac{1}{5}+\frac{1}{8}=\frac{8}{40}+\frac{5}{40}=\frac{13}{40}$
$\frac{4}{7}-\frac{1}{3}=\frac{12}{21}-\frac{7}{21}=\frac{5}{21}$

2. 下列算式的结果分别与哪个数最接近?估一估,连一连。
$\frac{4}{5}+\frac{1}{4}$ $\frac{1}{5}-\frac{1}{15}$ $\frac{6}{7}-\frac{1}{3}$

$\frac{4}{5}+\frac{1}{4}=\frac{16}{20}+\frac{5}{20}=\frac{21}{20}=1\frac{1}{20}$，与1最接近；
$\frac{1}{5}-\frac{1}{15}=\frac{3}{15}-\frac{1}{15}=\frac{2}{15}$，与0最接近；
$\frac{6}{7}-\frac{1}{3}=\frac{18}{21}-\frac{7}{21}=\frac{11}{21}$，与$\frac{1}{2}$最接近；
连线：
$\frac{4}{5}+\frac{1}{4}$ —— 1
$\frac{1}{5}-\frac{1}{15}$ —— 0
$\frac{6}{7}-\frac{1}{3}$ —— $\frac{1}{2}$

3. 算一算,填一填。

$\boxed{\begin{array}{l}\boldsymbol{\frac{1}{12}}\\ \boldsymbol{\_\_\_\_\_\_}\end{array}} \boldsymbol{\xrightarrow{+\frac{3}{8}}} \boxed{\begin{array}{l}\boldsymbol{\_\_\_\_\_\_}\\ \boldsymbol{\frac{3}{4}}\end{array}}$ $\boxed{\begin{array}{l}\boldsymbol{\frac{5}{12}}\\ \boldsymbol{\_\_\_\_\_\_}\end{array}} \boldsymbol{\xrightarrow{-\frac{1}{4}}} \boxed{\begin{array}{l}\boldsymbol{\_\_\_\_\_\_}\\ \boldsymbol{\frac{13}{20}}\end{array}}$

$\frac{1}{12} + \frac{3}{8} = \frac{2}{24} + \frac{9}{24} = \frac{11}{24}$
$\frac{3}{4} - \frac{3}{8} = \frac{6}{8} - \frac{3}{8} = \frac{3}{8}$
$\frac{5}{12} - \frac{1}{4} = \frac{5}{12} - \frac{3}{12} = \frac{1}{6}$
$\frac{13}{20} + \frac{1}{4} = \frac{13}{20} + \frac{5}{20} = \frac{9}{10}$
$\boxed{\begin{array}{l}\frac{1}{12}\\ \boldsymbol{\frac{3}{8}}\end{array}} \xrightarrow{+\frac{3}{8}} \boxed{\begin{array}{l}\boldsymbol{\frac{11}{24}}\\ \frac{3}{4}\end{array}}$
$\boxed{\begin{array}{l}\frac{5}{12}\\ \boldsymbol{\frac{9}{10}}\end{array}} \xrightarrow{-\frac{1}{4}} \boxed{\begin{array}{l}\boldsymbol{\frac{1}{6}}\\ \frac{13}{20}\end{array}}$

4. 小芳做数学作业用了$\frac{1}{3}$时,比做语文作业少用$\frac{1}{12}$时。小芳做语文作业用了多长时间?做语文作业和数学作业一共用了多长时间?

$\frac{1}{3} + \frac{1}{12} = \frac{4}{12} + \frac{1}{12} = \frac{5}{12}$（时）
$\frac{5}{12} + \frac{1}{3} = \frac{5}{12} + \frac{4}{12} = \frac{9}{12} = \frac{3}{4}$（时）
答：小芳做语文作业用了$\frac{5}{12}$时，做语文作业和数学作业一共用了$\frac{3}{4}$时。