# This may seem simple to you, but...

### This may seem simple to you, but...

Hi
I have stumbled over this math problem in something I am researching and would appreciate any clarification that anyone can give.
Most likely it is incredibly easy but also maybe not.
In ancient Indian astronomy, they have this concept of planetary periods.
Based on a 120-year cycle they say that there are 9 periods of different length (in total 120 years) where the 9 planets known to them have some special function. The periods are 7, 20, 6, 10, 7, 18, 16 and 19 years long in that order. They say everyone starts life in the balance of one of those periods and the remaining sequence is then fixed according to the list. So you can be born at the beginning, middle or end of one of those periods and when the period ends the next period starts after the balance of remaining time has elapsed. Since the total sequence is 120 years long and then starts again a person would only experience all the periods if they were to live for 120 years. If you were to live for 240 years then you would experience all periods twice.
What I am trying to figure out is how much of the world population would on average be found to be in the specifically 18 year period at any given time, taking that the average age of the world population is about 72 years, which means that hardly anyone would experience the full range of the cycle.
The determining factor for where a person starts in the cycle depends on the time of birth in relation to the lunar cycle at that time. But I don't think this is relevant for the calculation.
So there you have it.

Look forward to any ideas or ventures at a solution