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 $26\times\frac{5}{39}$

 $=\frac{2\times5}{3}$

 $=\frac{10}{3}$

 $\frac{24}{35}\times\frac{21}{20}$

 $=\frac{6\times3}{5\times5}$

 $=\frac{18}{25}$

 $\frac{15}{16}\times\frac{4}{3}\times\frac{8}{5}$

 $=\frac{5}{4}\times\frac{8}{5}$

 $=2$

 $9\div\frac{6}{13}\times\frac{4}{39}$

 $=9\times\frac{13}{6}\times\frac{4}{39}$

 $=9\times(\frac{13}{6}\times\frac{4}{39})$

 $=9\times\frac{2}{9}$

 $=2$

 $\frac{3}{5}\div6\times\frac{10}{9}$

 $=\frac{3}{5}\times\frac{1}{6}\times\frac{10}{9}$

 $=\frac{1}{10}\times\frac{10}{9}$

 $=\frac{1}{9}$

 $\frac{7}{8}\div\frac{21}{25}\div\frac{5}{16}$

 $=\frac{7}{8}\times\frac{25}{21}\times\frac{16}{5}$

 $=\frac{25}{24}\times\frac{16}{5}$

 $=\frac{10}{3}$

 $$根據(jù)乘法分配律a× c + b× c=(a + b)× c，這里a=\frac{4}{5}，b = \frac{11}{5}，c=\frac{7}{12}。
則\frac{7}{12}×\frac{4}{5}+\frac{11}{5}×\frac{7}{12}=\frac{7}{12}×(\frac{4}{5}+\frac{11}{5})。
先算括號(hào)里\frac{4}{5}+\frac{11}{5}=\frac{4 + 11}{5}=\frac{15}{5}=3。
再算\frac{7}{12}×3=\frac{7}{4}。$$

$解：根據(jù)(a + b)÷ c=a÷ c + b÷ c（c\neq0），這里a = 21，b=\frac{7}{12}，c=\frac{7}{3}。則(21+\frac{7}{12})÷\frac{7}{3}=21÷\frac{7}{3}+\frac{7}{12}÷\frac{7}{3}。因?yàn)?1÷\frac{7}{3}=21×\frac{3}{7}=9，\frac{7}{12}÷\frac{7}{3}=\frac{7}{12}×\frac{3}{7}=\frac{1}{4}。所以21÷\frac{7}{3}+\frac{7}{12}÷\frac{7}{3}=9+\frac{1}{4}=9\frac{1}{4}。$

$解：$

$把34寫成(33 + 1)。$

$根據(jù)乘法分配律(a + b)× c=a× c + b× c$

$（這里a = 33，b = 1，c=\frac{32}{33}）。$

$則\frac{32}{33}×34=\frac{32}{33}×(33 + 1)。$

$=\frac{32}{33}×33+\frac{32}{33}×1。$

$=32+\frac{32}{33}。$

$=32\frac{32}{33}。$

$解：先算小括號(hào)里\frac{3}{4}-\frac{2}{5}=\frac{15-8}{20}=\frac{7}{20}。再算中括號(hào)里1-\frac{7}{20}=\frac{20 - 7}{20}=\frac{13}{20}。最后算\frac{13}{20}×\frac{25}{26}=\frac{13×25}{20×26}=\frac{5}{8}。$

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