12. 直接写得数。
$\frac {1}{6}-\frac {1}{7}= $ $\frac {4}{9}+\frac {5}{6}= $ $\frac {7}{8}-\frac {1}{2}= $ $\frac {4}{7}-\frac {1}{3}= $
$\frac {2}{3}+\frac {5}{6}= $ $\frac {1}{5}+\frac {1}{2}= $ $\frac {6}{7}-\frac {2}{7}= $ $\frac {1}{16}+\frac {7}{8}= $
$\frac {1}{6}-\frac {1}{7}= $ $\frac {4}{9}+\frac {5}{6}= $ $\frac {7}{8}-\frac {1}{2}= $ $\frac {4}{7}-\frac {1}{3}= $
$\frac {2}{3}+\frac {5}{6}= $ $\frac {1}{5}+\frac {1}{2}= $ $\frac {6}{7}-\frac {2}{7}= $ $\frac {1}{16}+\frac {7}{8}= $
答案:
$\frac{1}{42}$ $\frac{23}{18}$ $\frac{3}{8}$ $\frac{5}{21}$ $\frac{3}{2}$ $\frac{7}{10}$ $\frac{4}{7}$ $\frac{15}{16}$
13. 解方程。
$\frac {9}{10}-x= \frac {1}{5}$ $\frac {6}{7}-x= \frac {5}{6}$ $x-(\frac {2}{3}+\frac {1}{4})= \frac {1}{12}$ $x-(\frac {1}{5}-\frac {1}{6})= \frac {11}{10}$
$\frac {9}{10}-x= \frac {1}{5}$ $\frac {6}{7}-x= \frac {5}{6}$ $x-(\frac {2}{3}+\frac {1}{4})= \frac {1}{12}$ $x-(\frac {1}{5}-\frac {1}{6})= \frac {11}{10}$
答案:
$x=\frac{7}{10}$ $x=\frac{1}{42}$ $x=1$ $x=\frac{17}{15}$
14. 脱式计算。(能简算的要简算)
$\frac {10}{13}-\frac {5}{9}+\frac {3}{13}$ $10-\frac {7}{11}-\frac {4}{11}$ $\frac {1}{7}+(\frac {5}{24}-\frac {1}{12})$ $\frac {9}{7}+\frac {3}{11}+\frac {3}{11}+\frac {5}{7}$
$\frac {10}{13}-\frac {5}{9}+\frac {3}{13}$ $10-\frac {7}{11}-\frac {4}{11}$ $\frac {1}{7}+(\frac {5}{24}-\frac {1}{12})$ $\frac {9}{7}+\frac {3}{11}+\frac {3}{11}+\frac {5}{7}$
答案:
$\frac{4}{9}$ 9 $\frac{15}{56}$ $2\frac{6}{11}$
15. 看图列式计算。
(2)

(2)
答案:
(1)$\frac{3}{9}+\frac{4}{9}+\frac{1}{9}=\frac{8}{9}$(千米)
(2)$3\frac{1}{3}-2\frac{1}{2}=\frac{5}{6}$(小时)
(1)$\frac{3}{9}+\frac{4}{9}+\frac{1}{9}=\frac{8}{9}$(千米)
(2)$3\frac{1}{3}-2\frac{1}{2}=\frac{5}{6}$(小时)
16. 修路队第一天修了$\frac {1}{8}$千米,比第二天少修了$\frac {3}{4}$千米,第三天比第一天多修了$\frac {1}{16}$千米。三天一共修了多少千米?
答案:
$\frac{1}{8}+\frac{3}{4}=\frac{7}{8}$(千米) $\frac{1}{8}+\frac{1}{16}=\frac{3}{16}$(千米) $\frac{1}{8}+\frac{7}{8}+\frac{3}{16}=1\frac{3}{16}$(千米)
17. 乐乐家有 1 升果汁,爸爸喝了$\frac {1}{3}$升,妈妈喝了$\frac {1}{5}$升,乐乐喝了$\frac {1}{3}$升。
(1)三人一共喝了多少升果汁? (2)还剩多少升果汁?
(1)三人一共喝了多少升果汁? (2)还剩多少升果汁?
答案:
(1)$\frac{1}{3}+\frac{1}{5}+\frac{1}{3}=\frac{13}{15}$(升)
(2)$1-\frac{13}{15}=\frac{2}{15}$(升)
(1)$\frac{1}{3}+\frac{1}{5}+\frac{1}{3}=\frac{13}{15}$(升)
(2)$1-\frac{13}{15}=\frac{2}{15}$(升)
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