We consider a wireless sensor network consisting of n sensors, each having a recorded bit, sensors measurement, which has been set to either 0 or 1. network has a special node called fusion center whose goal is to compute a symmetric function of these bits; i.e., a function that depends only on number of sensors that have a 1. sensors convey information to fusion center in a multi-hop fashion to enable function computation. problem studied is to minimize total transmission energy used by network when computing this function, subject to constraint that this computation is correct with high probability. We assume wireless channels are binary symmetric channels with a probability of error p, and that each sensor uses rαunits of energy to transmit each bit, where r is transmission range of sensor. main result in this paper is an algorithm whose energy usage is Θ (n(loglogn)(logn/n)α), and we also show that any algorithm satisfying performance constraints must necessarily have energy usage Ω (n(logn/n)α). Then, we consider case where sensor network observes N events, and each node records one bit per event, thus having N bits to convey. fusion center now wants to compute N symmetric functions, one for each of events.