Cool lecture on exponential growth http://sciencehack.com/videos/view/F-QA2rkpBSY The video shows how to calculate the doubling time by dividing 70 by the growth rate. So for a 7% growth rate, the doubling time is 10 years.
Some tutorials that helped me learn the Rubik's Cube: http://sciencehack.com/pages/page015
I'd like more complex ones though with a focus on strategy and speed cubing. Any ideas?