Subtract:

$\dfrac{-2}{5}$ from $\dfrac{-5}{7}$

To subtract one rational number from another, add the additive inverse of the rational number to be subtracted.

Subtracting $\dfrac{-2}{5}$ from $\dfrac{-5}{7}$,

LCM of 7 and 5 = 35

$\dfrac{-5}{7} - \left(\dfrac{-2}{5}\right) = \dfrac{-5}{7} + \dfrac{2}{5} \\[1em] = \dfrac{(-5) \times 5 + 2 \times 7}{35} \\[1em] = \dfrac{-25 + 14}{35} \\[1em] = \dfrac{-11}{35}$

Hence, the required difference is $\mathbf{\dfrac{-11}{35}}$.