1. The problem statement, all variables and given/known data A generation is about one-third of a lifetime. Approximately how many generations have passed since the year 0 AD? Let me first say that this is my first time taking physics and this is all new to me so I appreciate all the help. 2. Relevant equations here is the answer I found by googleing but I don't quite understand it. I was wondering if someone could explain it to me. history x (10^11s / history) × (1 generation / 1/3 lifetime) × (0.5 lifetime / 10^9s) = 150 3. The attempt at a solution How I approached this problem was that I chose 70 to be an average person's lifetime then I divided that by 3 to find what a generation is and then divide 2015 by that number which is not what the answer says. I think I just don't get the question.