12. 解方程。
$\frac {5}{6}-x= \frac {7}{9}$ $\frac {7}{16}+x= \frac {2}{3}$ $\frac {7}{10}-x= \frac {2}{5}$ $x+\frac {5}{9}-\frac {1}{6}= \frac {7}{12}$
$\frac {5}{6}-x= \frac {7}{9}$ $\frac {7}{16}+x= \frac {2}{3}$ $\frac {7}{10}-x= \frac {2}{5}$ $x+\frac {5}{9}-\frac {1}{6}= \frac {7}{12}$
答案:
$x=\frac{1}{18}$ $x=\frac{11}{48}$ $x=\frac{3}{10}$ $x=\frac{7}{36}$
13. 脱式计算。(能简算的要简算)
$\frac {4}{5}+\frac {3}{10}-\frac {4}{15}$ $2\frac {1}{3}-\frac {2}{7}-\frac {5}{7}$ $\frac {7}{12}-\frac {7}{9}+\frac {5}{12}$ $\frac {5}{8}+\frac {7}{18}-\frac {3}{8}+\frac {11}{18}$
$\frac {4}{5}+\frac {3}{10}-\frac {4}{15}$ $2\frac {1}{3}-\frac {2}{7}-\frac {5}{7}$ $\frac {7}{12}-\frac {7}{9}+\frac {5}{12}$ $\frac {5}{8}+\frac {7}{18}-\frac {3}{8}+\frac {11}{18}$
答案:
$\frac{5}{6}$ 1$\frac{1}{3}$ $\frac{2}{9}$ 1$\frac{1}{4}$
14. 看图列式计算。

答案:
$1\frac{1}{6}-\frac{1}{5}+1\frac{1}{6}=2\frac{2}{15}$(千米)
15. 列式计算。
(1)20 减去$\frac {5}{6}与\frac {1}{3}$的和,差是多少? (2)$\frac {7}{9}与\frac {1}{6}的和比\frac {1}{2}$多多少?
(1)20 减去$\frac {5}{6}与\frac {1}{3}$的和,差是多少? (2)$\frac {7}{9}与\frac {1}{6}的和比\frac {1}{2}$多多少?
答案:
(1)$20-(\frac{5}{6}+\frac{1}{3})=18\frac{5}{6}$
(2)$\frac{7}{9}+\frac{1}{6}-\frac{1}{2}=\frac{4}{9}$
(1)$20-(\frac{5}{6}+\frac{1}{3})=18\frac{5}{6}$
(2)$\frac{7}{9}+\frac{1}{6}-\frac{1}{2}=\frac{4}{9}$
16. 有甲、乙两壶水,甲壶重$\frac {3}{4}kg$,如果倒给乙壶$\frac {1}{4}kg$,那么两壶水同样重,两壶水共重多少千克?
答案:
$\frac{3}{4}-\frac{1}{4}=\frac{1}{2}$(kg),$\frac{1}{2}+\frac{1}{2}=1$(kg)
17. 一杯牛奶,小华喝了$\frac {1}{4}$后,又喝了剩下的$\frac {1}{3}$。小华一共喝了多少杯牛奶?
答案:
$\frac{1}{2}$杯
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