$\left(\dfrac 25\right)^{-3} = \dfrac{1}{\left(\frac 25\right)^3} = \dfrac{1}{\frac 8{125}} = \dfrac {125}8$
I'm not sure if my intuition about the above is correct, but here goes:
My intuition tells me that since we are taking the reciprocal of a fraction, the numerator of the "higher fraction" ($1$) is the whole of the denominator of the "lower fraction" ($125$), and so we can move the denominator of the lower fraction as the numerator of the higher fraction, because $1$ is practically the same as $125$.
What I can't seem to grasp is then why does the numerator of the lower fraction ($8$) become the denominator of the new fraction?
My question is very much like this one, but rotated.