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第52页

信息发布者：

 $\begin{aligned}&(\frac{2}{3}+\frac{2}{7})\div(\frac{8}{3}+\frac{8}{7})\\=&(\frac{2}{3}+\frac{2}{7})\div[(\frac{2}{3}+\frac{2}{7})\times4]\\=&(\frac{2}{3}+\frac{2}{7})\div(\frac{2}{3}+\frac{2}{7})\div4\\=&1\div4\\=&\frac{1}{4}\end{aligned}$

 $\begin{aligned}&42\div(\frac{1}{6}+\frac{1}{7})\\=&42\div\frac{13}{42}\\=&42\times\frac{42}{13}\\=&\frac{1764}{13}\end{aligned}$

 $\begin{aligned}&\frac{41}{42}\div\frac{1}{85}\\=&\frac{41}{42}\times85\\=&\frac{41}{42}\times(84 + 1)\\=&\frac{41}{42}\times84+\frac{41}{42}\times1\\=&82+\frac{41}{42}\\=&82\frac{41}{42}\end{aligned}$

 $\begin{aligned}&6\times(\frac{2}{3}-\frac{7}{16})\times32\\=&6\times\frac{2}{3}\times32-6\times\frac{7}{16}\times32\\=&128 - 84\\=&44\end{aligned}$

 $\begin{aligned}&\frac{1}{2}\div\frac{4}{5}+\frac{1}{2}\div\frac{1}{5}\\=&\frac{1}{2}\times\frac{5}{4}+\frac{1}{2}\times5\\=&\frac{5}{8}+\frac{5}{2}\\=&\frac{5}{8}+\frac{20}{8}\\=&\frac{25}{8}\end{aligned}$

 $\begin{aligned}&7\times\frac{5}{19}+14\times\frac{7}{19}\\=&5\times\frac{7}{19}+14\times\frac{7}{19}\\=&(5 + 14)\times\frac{7}{19}\\=&19\times\frac{7}{19}\\=&7\end{aligned}$

 $\begin{aligned}x-\frac{x}{4}&=\frac{1}{2}\\\frac{3}{4}x&=\frac{1}{2}\\x&=\frac{1}{2}\div\frac{3}{4}\\x&=\frac{1}{2}\times\frac{4}{3}\\x&=\frac{2}{3}\end{aligned}$

 $\begin{aligned}\frac{6}{7}x\div\frac{2}{3}&=\frac{8}{5}\\\frac{6}{7}x&=\frac{8}{5}\times\frac{2}{3}\\\frac{6}{7}x&=\frac{16}{15}\\x&=\frac{16}{15}\div\frac{6}{7}\\x&=\frac{16}{15}\times\frac{7}{6}\\x&=\frac{56}{45}\end{aligned}$

$280×(1-\frac {1}{4})=210($页$)$

答：一共看了$210$页。

$240×(\frac {1}{6}+\frac {3}{8})=130($页$)$

$130+1=131($页$)$

答：第三天应从第$131$页看起。

$72×(1-\frac {3}{8})=45($千米$/$时$)$

$45＜50$

答：能。

$28000×(\frac {2}{7}×4-1)=4000($台$)$

答：全年可以超产$4000$台。

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