I don't see how this formula works.
Lets say you have 100 dollars and you earn 40% each year.
According to formula you need years to double the money. Approximately 2 years according to formula.
But that is not correct. You need 3 years to double that money.
After first year you have 140 dollars, after second 196 and after third 274 dollars. So, you need 3 years.
Formula doesn't work.