1.下面各题算得对吗？正确的画“√”，错误的画“×”，并改正。
(1)$\frac{3}{5} - \frac{2}{5} × \frac{1}{2} = \frac{1}{5} × \frac{1}{2} = \frac{1}{10}$()
(2)$\frac{5}{7} × (1 - \frac{4}{7}) = \frac{5}{7} - \frac{4}{7} = \frac{1}{7}$()

(1) ×，改正：$\frac{3}{5}-\frac{2}{5}×\frac{1}{2}=\frac{3}{5}-\frac{1}{5}=\frac{2}{5}$
(2) ×，改正：$\frac{5}{7}×(1-\frac{4}{7})=\frac{5}{7}×\frac{3}{7}=\frac{15}{49}$

2.运用运算律进行简便计算,将算式补充完整。
(1)$\frac{6}{5}×\frac{7}{8}×\frac{5}{6}=$ ○ ○
(2)$\frac{5}{12}×\frac{2}{3}+\frac{5}{12}×\frac{1}{3}=$ ○ ( ○ )
(3)$(\frac{5}{8}+\frac{3}{4})×12=$ ○ ○ ○
(4)$\frac{9}{10}-\frac{2}{3}×\frac{9}{10}=$ ( ○ ) ○

(1) $\frac{6}{5} × \frac{5}{6} × \frac{7}{8}$
(2) $\frac{5}{12} × ( \frac{2}{3} + \frac{1}{3} )$
(3) $\frac{5}{8} × 12 + \frac{3}{4} × 12$
(4) $( 1 - \frac{2}{3} ) × \frac{9}{10}$

3.运用运算律进行简便计算,并说一说运用了什么运算律。
$\frac{33}{4}×\frac{3}{5}×\frac{12}{11}$
$(\frac{1}{6}+\frac{1}{8})×24$
$43×\frac{19}{42}$
$\frac{7}{20}×99+\frac{7}{20}$
$\frac{13}{5}×\frac{3}{13}-\frac{3}{13}×\frac{8}{5}$
$\frac{5}{12}×\frac{6}{25}×2.4×0.75$

$\frac{33}{4}×\frac{3}{5}×\frac{12}{11}$
$=\frac{33}{4}×\frac{12}{11}×\frac{3}{5}$
$=9×\frac{3}{5}$
$=\frac{27}{5}$，运用乘法交换律
$(\frac{1}{6}+\frac{1}{8})×24$
$=\frac{1}{6}×24+\frac{1}{8}×24$
$=4+3$
$=7$，运用乘法分配律
$43×\frac{19}{42}$
$=(42+1)×\frac{19}{42}$
$=42×\frac{19}{42}+1×\frac{19}{42}$
$=19+\frac{19}{42}$
$=19\frac{19}{42}$，运用乘法分配律
$\frac{7}{20}×99+\frac{7}{20}$
$=\frac{7}{20}×(99+1)$
$=\frac{7}{20}×100$
$=35$，运用乘法分配律
$\frac{13}{5}×\frac{3}{13}-\frac{3}{13}×\frac{8}{5}$
$=(\frac{13}{5}-\frac{8}{5})×\frac{3}{13}$
$=1×\frac{3}{13}$
$=\frac{3}{13}$，运用乘法分配律
$\frac{5}{12}×\frac{6}{25}×2.4×0.75$
$=\frac{5}{12}×\frac{6}{25}×\frac{12}{5}×\frac{3}{4}$
$=\frac{5}{12}×\frac{12}{5}×\frac{6}{25}×\frac{3}{4}$
$=\frac{9}{50}$，运用乘法交换律和结合律