[tex]\displaystyle\bf\\a=2\frac{1}{2}\\\\b=~0,\!5\\\\\frac{a}{b}=\frac{2\dfrac{1}{2}}{0,\!5}=\frac{~~\dfrac{2\times2+1}{2}~~}{\dfrac{1}{2}}=\frac{\dfrac{5}{2}}{\dfrac{1}{2}}=\dfrac{5}{2}\times\dfrac{2}{1}=\dfrac{5\times2}{2\times1}=\boxed{\bf5}[/tex]