The quickest way to remember the doubling time if you know the rate of growth (provided it is constant) is to remember this formula:
T2 = 70/rate
You can ask me how did I get this. Its simple, just take the use of exponential function. .7 is nothing but the natural log of 2 to base e.
Example: if you have $10,000 in the bank with a constant rate of growth, say 3%. So, when do you think you could get the double amount?
70/3 = 23.3 years. So, in 23 years whatever you’ve invested will double.
