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第54页

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$=\frac {3}{18}-\frac {2}{18}$

$=\frac {1}{18}$

$=\frac {9}{12}+\frac {10}{12}$

$=\frac {19}{12}$

$=\frac {8}{8}-\frac {3}{8}$

$=\frac {5}{8}$

$=\frac {14}{21}+\frac {12}{21}$

$=\frac {26}{21}$

$=\frac {25}{35}-\frac {14}{35}$

$=\frac {11}{35}$

$=\frac {8}{6}+\frac {9}{6}$

$=\frac {17}{6}$

$\begin{aligned}解：x&=\frac {4}{5}+\frac {1}{3}\\x&=\frac {17}{15}\end{aligned}$

$\begin{aligned}解：x&=\frac {3}{2}-\frac {1}{3}\\x&=\frac {7}{6}\end{aligned}$

$\begin{aligned}解：x&=\frac {3}{10}+\frac {4}{5}\\x&=\frac {11}{10}\end{aligned}$

$\begin{aligned}解：x&=\frac {5}{6}-\frac {1}{2}\\x&=\frac {1}{3}\end{aligned}$

$\begin{aligned}解：x&=\frac {7}{10}+\frac {1}{5}\\x&=\frac {9}{10}\end{aligned}$

$\begin{aligned}解：x&=\frac {2}{3}-\frac {2}{7}\\x&=\frac {8}{21}\end{aligned}$

$\frac {1}{2}+\frac {7}{10}=\frac {6}{5}($吨)

答：大米一共有$\frac {6}{5}$吨。

解：设晨晨在星期六用$x$小时进行体育锻炼，

$x-\frac {4}{5}=\frac {1}{6}，$

解得$x=\frac {29}{30}，$

答：晨晨在星期六用$\frac {29}{30}$小时进行体育锻炼.

$\frac {1}{8}+\frac {1}{12}=\frac {5}{24}$

答：两对合作一天能铺设这条管道的$\frac {5}{24}.$

$\frac {1}{8}-\frac {1}{12}=\frac {1}{24}$

答：两对合作一天，甲队比乙队多铺这条管道的$\frac {1}{24}.$