Subtract $ \dfrac{2}{r} $ from $ \dfrac{1}{5} $ to get $ \dfrac{ \color{purple}{ r-10 } }{ 5r }$.

To subtract raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the first fraction by $ \color{blue}{ r }$ and the second by $\color{blue}{ 5 }$.

$$ \begin{aligned} \frac{1}{5} - \frac{2}{r} & = \frac{ 1 \cdot \color{blue}{ r }}{ 5 \cdot \color{blue}{ r }} - \frac{ 2 \cdot \color{blue}{ 5 }}{ r \cdot \color{blue}{ 5 }} = \\[1ex] &=\frac{ \color{purple}{ r } }{ 5r } - \frac{ \color{purple}{ 10 } }{ 5r }=\frac{ \color{purple}{ r-10 } }{ 5r } \end{aligned} $$