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第24页

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$\begin {aligned}解：\frac {1}{4}x&=80\\x &=320\end {aligned}$

$\begin {aligned}解：2000x&=8\\x &=\frac {1}{250}\end {aligned}$

$\begin {aligned}解：\frac {9}{10}x&=\frac {3}{5}×\frac {2}{3}\\\frac {9}{10}x&=\frac {2}{5}\\x &=\frac {4}{9}\end {aligned}$

$=0.25×(\frac {4}{5}+3.2)$

$=0.25×4$

$=1$

$=(\frac {13}{5}×\frac {8}{13})×(8×1.25)$

$=\frac {8}{5}×10$

$=16$

$=4-\frac {1}{5}-\frac {4}{5}$

$=4-1$

$=3$

$=\frac {3}{8}÷\frac {3}{8}÷\frac {9}{20}$

$=\frac {20}{9}$