Since $\frac{1}{5}$ and $\frac{2}{5}$ have the same denominator, add them by adding their numerators.
$$\frac{5}{a}+\frac{1+2}{5}$$
Add $1$ and $2$ to get $3$.
$$\frac{5}{a}+\frac{3}{5}$$
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $a$ and $5$ is $5a$. Multiply $\frac{5}{a}$ times $\frac{5}{5}$. Multiply $\frac{3}{5}$ times $\frac{a}{a}$.
$$\frac{5\times 5}{5a}+\frac{3a}{5a}$$
Since $\frac{5\times 5}{5a}$ and $\frac{3a}{5a}$ have the same denominator, add them by adding their numerators.
