The Rule of 72(horsesaysinternet.com)
horsesaysinternet.com
The Rule of 72
http://www.horsesaysinternet.com/other/the-rule-of-72/
1 comments
There's an interesting lecture from Albert Bartlett [] on the same subject, but he uses the value of 70 to calculate the years to double.
[] http://www.youtube.com/watch?v=F-QA2rkpBSY