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第68頁

信息發(fā)布者：

?$\frac {7}{12}$?

?$\frac 45$?

?$\frac 15$?

$\begin{aligned}解：x&=\frac {3}{5}-\frac {5}{9}\\x&=\frac {2}{45}\end{aligned}$

$\begin{aligned}解：x&=\frac {3}{8}+\frac {5}{12}\\x&=\frac {19}{24}\end{aligned}$

$\begin{aligned}解：x&=\frac {1}{6}+\frac {5}{12}\\x&=\frac {7}{12}\end{aligned}$

$\begin{aligned}解：x&=\frac {8}{9}-\frac {1}{3}\\x&=\frac {5}{9}\end{aligned}$

$\frac{13}{42}$

$\frac{20}{99}$

$\frac{23}{120}$

$\frac{1}{42}$

$\frac{2}{99}$

$\frac{7}{120}$

1

積

和或差

$\frac{17}{72}$

$\frac{1}{56}$

$\frac{12}{35}$

$\frac{3}{130}$

$\frac{17}{60}$

$\frac{7}{144}$

D

A

?$\frac 12+\frac 38+\frac {1}{10}=\frac {39}{40}$?

?$\frac {39}{40}＜1$?

答：五年級一班同學(xué)本學(xué)期沒有都閱讀課外書。

?$\frac 32$?

?$=\frac 12+(\frac 13+\frac 23)+(\frac 14+\frac 24+\frac 34)+…+(\frac {1}{12}+\frac {2}{12}+…+\frac {11}{12})$?

?$=\frac 12+\frac 22+\frac 32+…+\frac {11}{2}$?

?$=\frac {1+2+3…+11}2$?

?$=33$?

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