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$=\frac {1}{5}+\frac {1}{5}$

$=\frac {2}{5}$

$=(\frac {3}{4}+\frac {3}{4})-(\frac {2}{5}+\frac {3}{5})$

$=\frac {3}{2}-1$

$=\frac {1}{2}$

$=1-\frac {1}{2}+\frac {1}{2}-\frac {1}{4}+\frac {1}{4}-\frac {1}{8}+...+\frac {1}{64}-\frac {1}{128}$

$=1-\frac {1}{128}$

$=\frac {127}{128}$

$\begin {aligned}解：7.2x&=20×36\\7.2x&=720\\x &=100\end {aligned}$

$\begin {aligned}解：36+3x&=60\\3x&=24\\x &=8\end {aligned}$

$\begin {aligned}解：x&=5-\frac {3}{7}\\x &=4 \frac {4}{7}\end {aligned}$

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