Knowing there are 100,000,000,000 neurons in an average human brain, and 7,000 dendrites in each neuron, and neurons are connected to each other by dendrites and axon terminals, how many synapses are there in an average human brain? (I don't know how many axon terminals per neuron there are on average.)
The human neocortex contains approximately 1.5x10^14 synapses, connecting its 19–23 billion neurons.
Source: Pakkenberg, B., Pelvig, D., Marner, L., Bundgaard, M. J., Gundersen, H. J. G., Nyengaard, J. R., & Regeur, L. (2003). Aging and the human neocortex. Experimental Gerontology, 38(1-2), 95-99. doi:10.1016/S0531-5565(02)00151-1