$\begin{array}{l}
+ )\,\,\left( {\dfrac{3}{4} - 0,2} \right).\left( {0,4 - \dfrac{4}{5}} \right)\\
= \left( {\dfrac{3}{4} - \dfrac{1}{5}} \right).\left( {\dfrac{2}{5} - \dfrac{4}{5}} \right) = \left( {\dfrac{{15}}{{20}} - \dfrac{4}{{20}}} \right).\dfrac{{ - 2}}{5}\\
= \dfrac{{11}}{{20}}.\dfrac{{ - 2}}{5} = \dfrac{{11.\left( { - 2} \right)}}{{20.5}} = \dfrac{{11.\left( { - 2} \right)}}{{\left( { - 2} \right).\left( { - 10} \right).5}} = \dfrac{{11}}{{ - 50}} = \dfrac{{ - 11}}{{50}}\\
+ )\,\,\sqrt {\dfrac{{49}}{{100}}} = \sqrt {{{\left( {\dfrac{7}{{10}}} \right)}^2}} = \dfrac{7}{{10}}
\end{array}$
