[tex]\displaystyle\bf\\\overline{ab} = 5(a+b)\\\\10a+b=5a+5b\\\\10a-5a=5b-b\\\\5a=4b\\\\\frac{a}{b}=\frac{4}{5}\\\\ \text{\bf~a si b sunt cifre.}\\\\\implies~a=4~si~b=5\\\\\implies~\boxed{\bf~n=45}\\\\Verificare:\\\\\frac{45}{4+5}=\frac{45}{9}=5[/tex]
