Đáp án:
$\begin{array}{l}
a)1\dfrac{1}{{23}} + \dfrac{2}{{21}} - \dfrac{1}{{23}} + \dfrac{{19}}{{21}} + {2016^0}\\
= \left( {\dfrac{{24}}{{23}} - \dfrac{1}{{23}}} \right) + \left( {\dfrac{2}{{21}} + \dfrac{{19}}{{21}}} \right) + 1\\
= \dfrac{{23}}{{23}} + \dfrac{{21}}{{21}} + 1\\
= 3\\
b)\left[ {{{\left( { - 5} \right)}^2} + {{\left( { - 3} \right)}^3}} \right].{\left( { - \dfrac{1}{2}} \right)^3}.{\left( { - 2} \right)^2}.{\left( { - 1} \right)^{2020}}\\
= \left( {25 - 27} \right).\left( { - \dfrac{1}{8}} \right).4\\
= \left( { - 2} \right).\left( { - \dfrac{1}{8}} \right).4\\
= 1\\
c)\left( {\dfrac{1}{{\sqrt {625} }} + \dfrac{1}{5} + 1} \right):\left( {\dfrac{1}{{25}} - \dfrac{1}{{\sqrt {25} }} - 1} \right)\\
= \left( {\dfrac{1}{{25}} + \dfrac{1}{5} + 1} \right):\left( {\dfrac{1}{{25}} - \dfrac{1}{5} - 1} \right)\\
= \left( {\dfrac{1}{{25}} + \dfrac{5}{{25}} + 1} \right):\left( {\dfrac{1}{{25}} - \dfrac{5}{{25}} - 1} \right)\\
= \dfrac{{31}}{{25}}:\left( { - \dfrac{{29}}{{25}}} \right)\\
= \dfrac{{31}}{{25}}.\left( { - \dfrac{{25}}{{29}}} \right)\\
= \dfrac{{31}}{{29}}
\end{array}$
