  For a tripartite pure state superposed by two individual states, the
bipartitely shared entanglement can always be achieved by local measurements of
the third party. Consider the different aims of the third party, i.e.
maximizing or minimizing the bipartitely shared entanglement, we find bounds on
both the possible bipartitely shared entanglement of the superposition state in
terms of the corresponding entanglement of the two states being superposed. In
particular, by choosing the concurrence as bipartite entanglement measure, we
obtain calculable bounds for tripartite $(2\otimes 2\otimes n)$ -dimensional
cases.
