  We consider a "Social Group" of networked nodes, seeking a "universe" of
segments. Each node has subset of the universe, and access to an expensive
resource for downloading data. Alternatively, nodes can also acquire the
universe by exchanging segments among themselves, at low cost, using a local
network interface. While local exchanges ensure minimum cost, "free riders" in
the group can exploit the system. To prohibit free riding, we propose the
"Give-and-Take" criterion, where exchange is allowed if each node has segments
unavailable with the other. Under this criterion, we consider the problem of
maximizing the aggregate cardinality of the nodes' segment sets. First, we
present a randomized algorithm, whose analysis yields a lower bound on the
expected aggregate cardinality, as well as an approximation ratio of 1/4 under
some conditions. Four other algorithms are presented and analyzed. We identify
conditions under which some of these algorithms are optimal
