import math


def sanderson(radius: float, noble_gas_radius: float) -> float:
    """
    Calculate Sanderson's electronegativity

    Args:
        radius: radius value for the element
        noble_gas_radius: value of the radius of a hypothetical noble gas with
        the atomic number of element for which electronegativity is calculated

    .. math::

        \chi = \\frac{AD}{AD_{\\text{ng}}}

    """

    return math.pow(noble_gas_radius / radius, 3)