1. 填一填。
(1)$\frac{3}{8}×11×\frac{8}{3}= \frac{3}{8}×$×=
(2)$\frac{5}{8}×\frac{7}{10}+\frac{5}{8}×\frac{3}{10}= $×(+)=
(3)$(\frac{1}{5}+\frac{1}{8})×40= $×+×=
(4)$\frac{9}{10}×17-\frac{9}{10}×7= $×(-)=

(1)$\frac{8}{3}$，11，11
(2)$\frac{5}{8}$，$\frac{7}{10}$，$\frac{3}{10}$，$\frac{5}{8}$
(3)$\frac{1}{5}$，40，$\frac{1}{8}$，40，13
(4)$\frac{9}{10}$，17，7，9

2. 用简便方法计算下面各题。
$\frac{5}{6}×\frac{3}{7}×6$ $\frac{6}{7}×\frac{4}{9}×14$ $(\frac{2}{5}+\frac{3}{4})×60$
$24×(\frac{3}{4}-\frac{1}{2})$ $\frac{2}{7}×\frac{1}{4}+\frac{3}{4}×\frac{2}{7}$ $\frac{5}{7}-\frac{8}{15}×\frac{5}{7}$

1.
$\frac{5}{6} × \frac{3}{7} × 6$
$=\frac{5}{6} × 6 × \frac{3}{7}$
$= 5 × \frac{3}{7}$
$ = \frac{15}{7}$
$ = 2\frac{1}{7}$
2.
$\frac{6}{7} × \frac{4}{9} × 14$
$=\frac{6}{7} × 14 × \frac{4}{9}$
$ = 12 × \frac{4}{9}$
$ = \frac{16}{3}$
$ = 5\frac{1}{3}$
3.
$(\frac{2}{5} + \frac{3}{4}) × 60$
$=\frac{2}{5} × 60 + \frac{3}{4} × 60$
$ = 24 + 45$
$ = 69$
4.
$24 × (\frac{3}{4} - \frac{1}{2})$
$=24 × \frac{3}{4} - 24 × \frac{1}{2}$
$ = 18 - 12$
$ = 6$
5.
$\frac{2}{7} × \frac{1}{4} + \frac{3}{4} × \frac{2}{7}$
$=\frac{2}{7} × (\frac{1}{4} + \frac{3}{4})$
$ = \frac{2}{7} × 1$
$ = \frac{2}{7}$
6.
$\frac{5}{7} - \frac{8}{15} × \frac{5}{7}$
$=\frac{5}{7} × (1 - \frac{8}{15})$
$ = \frac{5}{7} × \frac{7}{15}$
$ = \frac{1}{3}$

3. 一个长方形,长是$\frac{3}{4}$m,宽是$\frac{1}{2}$m,这个长方形的周长是多少米？
用简便方法计算。
(1)$\frac{17}{25}×\frac{3}{50}×\frac{30}{51}×125$ (2)$\frac{4}{9}×3+\frac{2}{9}×2+\frac{1}{9}×2$

第一题：长方形周长
已知长方形长$a = \frac{3}{4}$m，宽$b=\frac{1}{2}$m，根据长方形周长公式$C=(a + b)×2$，可得：
$\begin{align}C&=(\frac{3}{4}+\frac{1}{2})×2\\&=(\frac{3}{4}+\frac{2}{4})×2\\&=\frac{5}{4}×2\\&=\frac{5}{2}(m)\end{align}$
(1) 计算$\frac{17}{25}×\frac{3}{50}×\frac{30}{51}×125$
$\begin{align}&\frac{17}{25}×\frac{3}{50}×\frac{30}{51}×125\\=&\frac{17}{25}×\frac{30}{51}×\frac{3}{50}×125\\=&\frac{2}{5}×\frac{3}{50}×125\\=&\frac{2}{5}×\frac{375}{50}\\=&\frac{2}{5}×\frac{15}{2}\\=& 3\end{align}$
(2) 计算$\frac{4}{9}×3+\frac{2}{9}×2+\frac{1}{9}×2$
$\begin{align}&\frac{4}{9}×3+\frac{2}{9}×2+\frac{1}{9}×2\\=&\frac{12}{9}+\frac{4}{9}+\frac{2}{9}\\=&\frac{12 + 4+2}{9}\\=&2\end{align}$
综上，长方形周长是$\frac{5}{2}$m；(1)式结果为$3$；(2)式结果为$2$。