  Within a mean field plus Random-Phase Approximation formalism, we investigate
the collective excitations of a three component Fermi-Bose mixture of K atoms,
magnetically trapped and subjected to repulsive s-wave interactions. We analyze
both the single-particle excitation and the density oscillation spectra created
by external multipolar fields, for varying fermion concentrations. The
formalism and the numerical output are consistent with the Generalized Kohn
Theorem for the whole multispecies system. The calculations give rise to
fragmented density excitation spectra of the fermion sample and illustrate the
role of the mutual interaction in the observed deviations of the bosonic
spectra with respect to Stringari's rule.
