4. 计算。
(1)直接写出得数。
$\frac {2}{3}×\frac {9}{8}=$ $6÷\frac {1}{3}=$ $\frac {3}{8}×3=$
$\frac {5}{4}×\frac {7}{15}=$ $28×\frac {5}{14}=$ $5÷\frac {1}{50}=$
(2)下面各题怎样简便就怎样算。
$\frac {5}{12}÷\frac {1}{8}+\frac {1}{12}×8$$=\frac5{12}×8+\frac1{12}×8$
$ =(\frac5{12}+\frac1{12})×8$
=4 $\frac {12}{5}×(\frac {5}{6}+\frac {3}{4})$$=\frac{12}5×\frac56+\frac{12}5×\frac34$
$ =2+\frac95$
$ =3\frac45$
$(\frac {1}{3}-\frac {1}{4})÷\frac {1}{12}$$=(\frac13-\frac14)×12$
$ =\frac13×12-\frac14×12$
=1 $\frac {4}{5}÷[(\frac {3}{4}-\frac {1}{6})×\frac {4}{7}]$$=\frac45÷[\frac7{12}×\frac47]$
$ =\frac45÷\frac13$
$ =\frac{12}5$

$\frac{3}{4}$
18
$1\frac{1}{8}$
$\frac{7}{12}$
10
250
$=\frac5{12}×8+\frac1{12}×8$
$ =(\frac5{12}+\frac1{12})×8$
=4
$=\frac{12}5×\frac56+\frac{12}5×\frac34$
$ =2+\frac95$
$ =3\frac45$
$=(\frac13-\frac14)×12$
$ =\frac13×12-\frac14×12$
=1
$=\frac45÷[\frac7{12}×\frac47]$
$ =\frac45÷\frac13$
$ =\frac{12}5$

5. 解下列方程。
$\frac {1}{12}x-\frac {2}{5}×\frac {5}{9}= \frac {3}{4}$ $x+\frac {1}{4}x= \frac {1}{4}$ $x÷\frac {5}{6}= \frac {3}{8}$

$ $解：$ \frac1{12}x=\frac34+\frac29$　　
$ \frac1{12}x=\frac{35}{36}$　　
$ x=\frac{35}3$　　
解：$ \frac54x=\frac14$　　
$ x=\frac15$　　
解：$ x=\frac38×\frac56$　　
$ x=\frac5{16}$　　

$\frac{1}{12}x - \frac{2}{5} × \frac{5}{9} = \frac{3}{4}$
$\frac{1}{12}x - \frac{2}{9} = \frac{3}{4}$
$\frac{1}{12}x = \frac{3}{4} + \frac{2}{9}$
$\frac{1}{12}x = \frac{27}{36} + \frac{8}{36}$
$\frac{1}{12}x = \frac{35}{36}$
$x = \frac{35}{36} × 12$
$x = \frac{35}{3}$
$x + \frac{1}{4}x = \frac{1}{4}$
$\frac{5}{4}x = \frac{1}{4}$
$x = \frac{1}{4} × \frac{4}{5}$
$x = \frac{1}{5}$
$x ÷ \frac{5}{6} = \frac{3}{8}$
$x = \frac{3}{8} × \frac{5}{6}$
$x = \frac{5}{16}$