  We analyze mixed multi-qubit states composed of a W class state and a product
state with all qubit in |0>. We find the optimal pure state decomposition and
convex roofs for higher-tangle with bipartite partition between one qubit and
the rest qubits for those mixed states. The optimality of the decomposition is
ensured by the Coffman-Kundu-Wootters (CKW) inequality which describes the
monogamy of quantum entanglement. The generalized monogamy inequality is found
to be true for W class states with arbitrary partitions between one qubit and
multi-qubit.
