Performing operations with fractional indices is fairly easy.
With fractional indices the numerator (top number of a fraction) remains the indice (exponent). The denominator (bottom number of a fraction) becomes the nth root.
In this example, the 27 is the base with 2/3 as the fractional exponent (indice). So you would rewrite this as the cube root of 27 to the power of 2.
Fractional Indice Videos
My Maths 10/10A