  In this paper, we evaluate the expectation values of four-quark operators for
the inclusive beauty decays from the differences in the inclusive total decay
rates, assuming that the heavy quark expansion converges at $O(1/m^3)$. The
obtained expectation values yeilds the ratio $\tau(\Lambda_b)/\tau(B)$ close to
the experimental onee. We further point out that the quark-hadron duality
violation would be rather small allowing predictions of inclusive quantities.
