2. 计算下面各题,怎样简便就怎样算。(12分)
$\frac{2}{5}÷(\frac{3}{4}+\frac{2}{5})$ $\frac{1}{2}×\frac{2}{5}+\frac{9}{10}÷\frac{9}{20}$
$24×\frac{5}{7}×\frac{7}{12}$ $(\frac{7}{8}+\frac{1}{6}+\frac{2}{3})×48$
$\frac{8}{13}÷7+\frac{1}{7}×\frac{6}{13}$ $(\frac{4}{5}-\frac{2}{3})÷\frac{8}{15}$

$\frac{2}{5}÷(\frac{3}{4}+\frac{2}{5})$
$=\frac{2}{5}÷(\frac{15}{20}+\frac{8}{20})$
$=\frac{2}{5}÷\frac{23}{20}$
$=\frac{2}{5}×\frac{20}{23}$
$=\frac{8}{23}$
$\frac{1}{2}×\frac{2}{5}+\frac{9}{10}÷\frac{9}{20}$
$=\frac{1}{5}+\frac{9}{10}×\frac{20}{9}$
$=\frac{1}{5}+2$
$=2\frac{1}{5}$
$24×\frac{5}{7}×\frac{7}{12}$
$=24×\frac{7}{12}×\frac{5}{7}$
$=14×\frac{5}{7}$
$=10$
$(\frac{7}{8}+\frac{1}{6}+\frac{2}{3})×48$
$=\frac{7}{8}×48+\frac{1}{6}×48+\frac{2}{3}×48$
$=42 + 8 + 32$
$=82$
$\frac{8}{13}÷7+\frac{1}{7}×\frac{6}{13}$
$=\frac{8}{13}×\frac{1}{7}+\frac{1}{7}×\frac{6}{13}$
$=(\frac{8}{13}+\frac{6}{13})×\frac{1}{7}$
$=\frac{14}{13}×\frac{1}{7}$
$=\frac{2}{13}$
$(\frac{4}{5}-\frac{2}{3})÷\frac{8}{15}$
$=(\frac{12}{15}-\frac{10}{15})×\frac{15}{8}$
$=\frac{2}{15}×\frac{15}{8}$
$=\frac{1}{4}$

3. 解方程。(6分)
$x÷\frac{5}{9}= \frac{18}{25}$ $x+\frac{7}{8}x= \frac{3}{4}$ $4x-6×\frac{2}{3}= 2$

$x÷\frac{5}{9}= \frac{18}{25}$
解：$x=\frac{18}{25}×\frac{5}{9}$
$x=\frac{2}{5}$
$x+\frac{7}{8}x= \frac{3}{4}$
解：$\frac{15}{8}x=\frac{3}{4}$
$x=\frac{3}{4}÷\frac{15}{8}$
$x=\frac{3}{4}×\frac{8}{15}$
$x=\frac{2}{5}$
$4x-6×\frac{2}{3}= 2$
解：$4x-4=2$
$4x=2+4$
$4x=6$
$x=6÷4$
$x=\frac{3}{2}$