Question

A molecule that can be used as a molecular clock has a neutral mutation rate of one mutation per 20 million years. How many years ago did two species share a common ancestor if the molecules found in these two species differ by a total of six mutations?

Answer 1

If there is one mutation after the first 20 million years, two mutations after the first 40 million years and so on, how many million years will have elapsed if there are six mutations?