  We study the entanglement feature of the ground state of a system composed of
spin 1 and 1/2 parts. The concurrence vector is shown to be consistent with the
measurement of von Neumann entropy for such system. In the light of the ground
state degeneracy, we suggest a average concurrence to measure the entanglement
of Hilbert subspace. The entanglement property of both a general superposition
as well as the mixture of the degenerate ground states are discussed by means
of average concurrence and the negativity respectively.
