We study probabilistic combinations of expanding dynamical systems, wh
ich we call expanding probabilistic dynamical systems, in one dimensio
n. If the system is composed by exact endomorphisms we prove that the
probabilistic dynamical system is an exact Markov semigroup, and we de
termine a generalized spectral decomposition of the associated Markov
operator on densities for an example of the tent map coupled with the
2-Renyi map. (C) 1998 Published by Elsevier Science B.V.