  A simple recipe to derive the compressibility factor of a multicomponent
mixture of d-dimensional additive hard spheres in terms of that of the
one-component system is proposed. The recipe is based (i) on an exact condition
that has to be satisfied in the special limit where one of the components
corresponds to point particles; and (ii) on the form of the radial distribution
functions at contact as obtained from the Percus-Yevick equation in the
three-dimensional system. The proposal is examined for hard discs and hard
spheres by comparison with well-known equations of state for these systems and
with simulation data. In the special case of d=3, our extension to mixtures of
the Carnahan-Starling equation of state yields a better agreement with
simulation than the already accurate Boublik-Mansoori-Carnahan-Starling-Leland
equation of state.
