What number should be subtracted from $-\dfrac{2}{3}$ to get $-\dfrac{1}{6}$?

[Hint: Required number = $\dfrac{-2}{3} - \left(-\dfrac{1}{6}\right)$]

Let the required number be $x$.

According to the given condition,

$\Rightarrow \dfrac{-2}{3} - x = \dfrac{-1}{6} \\[1em] \Rightarrow x = \dfrac{-2}{3} - \left(\dfrac{-1}{6}\right) \\[1em] \Rightarrow x = \dfrac{-2}{3} + \dfrac{1}{6} \\[1em] [\text{ LCM of } 3 \text{ and } 6 = 6] \\[1em] \Rightarrow x = \dfrac{(-2) \times 2 + 1}{6} \\[1em] \Rightarrow x = \dfrac{-4 + 1}{6} \\[1em] \Rightarrow x = \dfrac{-3}{6} = \dfrac{-1}{2}$

Hence, the required number is $\mathbf{\dfrac{-1}{2}}$.