Giải thích các bước giải:
$\begin{array}{l}
3\dfrac{1}{{417}}.\dfrac{1}{{762}} - \dfrac{1}{{139}}.4\dfrac{{761}}{{762}} - \dfrac{4}{{417.762}} + \dfrac{5}{{139}}\\
= 3\dfrac{1}{{417}}.\dfrac{1}{{762}} - \dfrac{1}{{139}}.\left( {5 - \dfrac{1}{{762}}} \right) - \dfrac{4}{{417.762}} + \dfrac{5}{{139}}\\
= 3\dfrac{1}{{417}}.\dfrac{1}{{762}} - \dfrac{5}{{139}} + \dfrac{1}{{139}}.\dfrac{1}{{762}} - \dfrac{4}{{417}}.\dfrac{1}{{762}} + \dfrac{5}{{139}}\\
= \left( {3\dfrac{1}{{417}}.\dfrac{1}{{762}} + \dfrac{1}{{139}}.\dfrac{1}{{762}} - \dfrac{4}{{417}}.\dfrac{1}{{762}}} \right) - \dfrac{5}{{139}} + \dfrac{5}{{139}}\\
= \dfrac{1}{{762}}\left( {3\dfrac{1}{{417}} + \dfrac{1}{{139}} - \dfrac{4}{{417}}} \right)\\
= \dfrac{1}{{762}}\left( {3 + \dfrac{1}{{417}} + \dfrac{3}{{417}} - \dfrac{4}{{417}}} \right)\\
= \dfrac{3}{{762}}\\
= \dfrac{1}{{254}}
\end{array}$
