1 直接写出得数。
$ \frac{3}{5} × 20 = $
$ \frac{5}{4} × \frac{2}{3} = $
$ \frac{5}{9} + \frac{1}{6} = $
$ 8 × \frac{1}{8} ÷ 8 × \frac{1}{8} = $
$ \frac{3}{5} × 20 = $
12
$ \frac{8}{9} × \frac{27}{32} = $$\frac{3}{4}$
$ \frac{5}{4} × \frac{2}{3} = $
$\frac{5}{6}$
$ \frac{1}{4} - \frac{1}{7} = $$\frac{3}{28}$
$ \frac{5}{9} + \frac{1}{6} = $
$\frac{13}{18}$
$ \frac{2}{7} ÷ \frac{6}{21} = $1
$ 8 × \frac{1}{8} ÷ 8 × \frac{1}{8} = $
$\frac{1}{64}$
$ \frac{1}{5} × 9 + 9 × \frac{4}{5} = $9
答案：12；$\frac{3}{4}$；$\frac{5}{6}$；$\frac{3}{28}$；$\frac{13}{18}$；1；$\frac{1}{64}$；9
$2 $计算下面各题$,$注意使用简便算法。
$ \frac{2}{7} × \frac{5}{9} × (36 × 28)$ $18 × (\frac{1}{2} + \frac{1}{3} - \frac{1}{6}) $
$ (\frac{5}{6} - \frac{7}{12} × \frac{15}{14}) ÷ \frac{5}{4}$ $\frac{7}{9} ÷ \frac{13}{5} + \frac{2}{9} × \frac{5}{13} $
$ \frac{2}{7} × \frac{5}{9} × (36 × 28)$ $18 × (\frac{1}{2} + \frac{1}{3} - \frac{1}{6}) $
$ (\frac{5}{6} - \frac{7}{12} × \frac{15}{14}) ÷ \frac{5}{4}$ $\frac{7}{9} ÷ \frac{13}{5} + \frac{2}{9} × \frac{5}{13} $
答案：1.
$ \begin{aligned}&\frac{2}{7} × \frac{5}{9} × (36 × 28)\\=&\frac{2}{7} × \frac{5}{9} × 36 × 28\\=&(\frac{2}{7} × 28) × (\frac{5}{9} × 36)\\=&8×20\\=&160\end{aligned} $
2.
$ \begin{aligned}&18× (\frac{1}{2} + \frac{1}{3} - \frac{1}{6})\\=&18×\frac{1}{2}+18×\frac{1}{3}-18×\frac{1}{6}\\=&9 + 6 - 3\\=&12\end{aligned} $
3.
$ \begin{aligned}&(\frac{5}{6} - \frac{7}{12} × \frac{15}{14}) ÷ \frac{5}{4}\\=&(\frac{5}{6} - \frac{5}{8}) ÷ \frac{5}{4}\\=&(\frac{20}{24} - \frac{15}{24}) ÷ \frac{5}{4}\\=&\frac{5}{24} ÷ \frac{5}{4}\\=&\frac{5}{24} × \frac{4}{5}\\=&\frac{1}{6}\end{aligned} $
4.
$ \begin{aligned}&\frac{7}{9} ÷ \frac{13}{5} + \frac{2}{9} × \frac{5}{13}\\=&\frac{7}{9} × \frac{5}{13} + \frac{2}{9} × \frac{5}{13}\\=&(\frac{7}{9} + \frac{2}{9}) × \frac{5}{13}\\=&1×\frac{5}{13}\\=&\frac{5}{13}\end{aligned} $
$ \begin{aligned}&\frac{2}{7} × \frac{5}{9} × (36 × 28)\\=&\frac{2}{7} × \frac{5}{9} × 36 × 28\\=&(\frac{2}{7} × 28) × (\frac{5}{9} × 36)\\=&8×20\\=&160\end{aligned} $
2.
$ \begin{aligned}&18× (\frac{1}{2} + \frac{1}{3} - \frac{1}{6})\\=&18×\frac{1}{2}+18×\frac{1}{3}-18×\frac{1}{6}\\=&9 + 6 - 3\\=&12\end{aligned} $
3.
$ \begin{aligned}&(\frac{5}{6} - \frac{7}{12} × \frac{15}{14}) ÷ \frac{5}{4}\\=&(\frac{5}{6} - \frac{5}{8}) ÷ \frac{5}{4}\\=&(\frac{20}{24} - \frac{15}{24}) ÷ \frac{5}{4}\\=&\frac{5}{24} ÷ \frac{5}{4}\\=&\frac{5}{24} × \frac{4}{5}\\=&\frac{1}{6}\end{aligned} $
4.
$ \begin{aligned}&\frac{7}{9} ÷ \frac{13}{5} + \frac{2}{9} × \frac{5}{13}\\=&\frac{7}{9} × \frac{5}{13} + \frac{2}{9} × \frac{5}{13}\\=&(\frac{7}{9} + \frac{2}{9}) × \frac{5}{13}\\=&1×\frac{5}{13}\\=&\frac{5}{13}\end{aligned} $
$3.$比一比，再解答
$(1)$食堂运来$ \frac{4}{5} $吨煤$,$用掉一些后还剩$ \frac{1}{5} ,$还剩多少吨$？$
$(2)$食堂运来$ \frac{4}{5} $吨煤$,$用掉$ \frac{1}{4} ,$还剩下多少吨$？$
$(3)$食堂运来$ \frac{4}{5} $吨煤$,$用掉$ \frac{2}{5} $后$,$又用掉$ \frac{1}{4} $吨$,$还剩下多少吨$？$
$(4)$食堂运来$ \frac{4}{5} $吨煤$,$用掉$ \frac{2}{5} $吨后$,$又用掉余下的$ \frac{1}{4} ,$还剩下多少吨$？$
$(1)$食堂运来$ \frac{4}{5} $吨煤$,$用掉一些后还剩$ \frac{1}{5} ,$还剩多少吨$？$
$(2)$食堂运来$ \frac{4}{5} $吨煤$,$用掉$ \frac{1}{4} ,$还剩下多少吨$？$
$(3)$食堂运来$ \frac{4}{5} $吨煤$,$用掉$ \frac{2}{5} $后$,$又用掉$ \frac{1}{4} $吨$,$还剩下多少吨$？$
$(4)$食堂运来$ \frac{4}{5} $吨煤$,$用掉$ \frac{2}{5} $吨后$,$又用掉余下的$ \frac{1}{4} ,$还剩下多少吨$？$
答案：(1)$ \frac{4}{5} × \frac{1}{5}=\frac{4}{25}（吨）$
(2)$ \frac{4}{5} × (1 - \frac{1}{4})=\frac{4}{5} × \frac{3}{4}=\frac{3}{5}（吨）$
(3)$ \begin{aligned}&\frac{4}{5} - \frac{4}{5} × \frac{2}{5} - \frac{1}{4}\\=&\frac{4}{5} - \frac{8}{25} - \frac{1}{4}\\=&\frac{20}{25} - \frac{8}{25} - \frac{1}{4}\\=&\frac{12}{25} - \frac{1}{4}\\=&\frac{48}{100} - \frac{25}{100}\\=&\frac{23}{100}（吨）\end{aligned} $
(4)
$ \begin{aligned}&(\frac{4}{5} - \frac{2}{5}) × (1 - \frac{1}{4})\\=&\frac{2}{5} × \frac{3}{4}\\=&\frac{3}{10}（吨）\end{aligned} $
(2)$ \frac{4}{5} × (1 - \frac{1}{4})=\frac{4}{5} × \frac{3}{4}=\frac{3}{5}（吨）$
(3)$ \begin{aligned}&\frac{4}{5} - \frac{4}{5} × \frac{2}{5} - \frac{1}{4}\\=&\frac{4}{5} - \frac{8}{25} - \frac{1}{4}\\=&\frac{20}{25} - \frac{8}{25} - \frac{1}{4}\\=&\frac{12}{25} - \frac{1}{4}\\=&\frac{48}{100} - \frac{25}{100}\\=&\frac{23}{100}（吨）\end{aligned} $
(4)
$ \begin{aligned}&(\frac{4}{5} - \frac{2}{5}) × (1 - \frac{1}{4})\\=&\frac{2}{5} × \frac{3}{4}\\=&\frac{3}{10}（吨）\end{aligned} $