5.
[tex]\it a)\ \ \dfrac{^{2)}2}{\ 5}=\dfrac{4}{10}=0,4\\ \\ \\ c)\ \ \dfrac{^{25)}1}{\ 4}=\dfrac{25}{100}=0,25\\ \\ \\ d)\ \ \dfrac{^{5)}3}{\ 20}=\dfrac{15}{100}=0,15[/tex]
6.
[tex]\it \overline{a,b}+\overline{b.a}=7,7|_{\cdot10} \Rightarrow \overline{ab}+\overline{ba}=77 \Rightarrow 10a+b+10b+a=77 \Rightarrow \\ \\ \Rightarrow 11a+11b=77|_{:11} \Rightarrow a+b=7[/tex]
