Đáp án:
$\begin{array}{l}
B1)\\
a)A = 3\dfrac{1}{7} - \left( {5.0,05 + \dfrac{{22}}{7}} \right) - \left( {4 + 0,75} \right)\\
= \dfrac{{22}}{7} - 0,25 - \dfrac{{22}}{7} - 4 - 0,75\\
= \left( { - 0,25 - 0,75} \right) - 4\\
= - 1 - 4\\
= - 5\\
b)B = \dfrac{{{{\left( { - 1} \right)}^{2018}}.{{\left( {\dfrac{2}{5}} \right)}^4}.{{\left( {\dfrac{{15}}{4}} \right)}^2}}}{{\dfrac{{{{15}^2}}}{{{2^8}}}.{{\left( {\dfrac{2}{5}} \right)}^3}}}\\
= \dfrac{{1.\dfrac{2}{5}.\dfrac{{{{15}^2}}}{{{2^4}}}}}{{\dfrac{{{{15}^2}}}{{{2^8}}}}} = \dfrac{2}{5}{.2^4} = \dfrac{{{2^5}}}{5}\\
B2)a){2^3}{.2^x} - 2,1 = 13,9\\
\Rightarrow {2^{3 + x}} = 13,9 + 2,1 = 16\\
\Rightarrow {2^{3 + x}} = {2^4}\\
\Rightarrow 3 + x = 4\\
\Rightarrow x = 1\\
\text{Vậy}\,x = 1\\
b)\left| {x - \dfrac{3}{2}} \right| = \sqrt {0,25} \\
\Rightarrow \left| {x - 1,5} \right| = 0,5\\
\Rightarrow \left[ \begin{array}{l}
x - 1,5 = 0,5\\
x - 1,5 = - 0,5
\end{array} \right.\\
\Rightarrow \left[ \begin{array}{l}
x = 2\\
x = 1
\end{array} \right.\\
\text{Vậy}\,x = 1;x = 2\\
c)\dfrac{x}{2} = \dfrac{y}{7}\\
= \dfrac{{2x}}{4} = \dfrac{{5y}}{{35}} = \dfrac{{2x - 5y}}{{4 - 35}} = \dfrac{{93}}{{ - 31}} = - 3\\
\Rightarrow \left\{ \begin{array}{l}
x = - 6\\
y = - 21
\end{array} \right.\\
\text{Vậy}\,x = - 6;y = - 21
\end{array}$
