4 ms·
Neat math trick from the video: 70 / x = number of years of constant growth required for a quantity to double given that it grows at x percent The example use
by jluxenberg 16y ago
Neat math trick from the video:
70 / x = number of years of constant growth required for a quantity to double given that it grows at x percent
The example used in the video: if the price of lift tickets goes up by 7% per year, in 10 years, that price will double.
(and actually, the constant 70 is an approximation, the actual constant is ln (2) * 100)
- chaosmachine 16y agoIt's also a useful way to tell when your investments will double in value. 5% interest: 70/5 = 14 years to double your money.
- Luc 16y agoIt also works for inflation or other yearly recurring charges. Those small percentages add up quickly - at 3% inflation and 2% charges the value of your investment in today's dollars/euros will halve in 14 years. Yikes!
- eru 16y agoYes, but why use it, when you can do a logarithm?
- sesqu 16y agoFew people can do logarithms in their heads - and those that can, usually do it using similar tricks. I realize that "doing math in your head" is well on the decline, but it is pretty essential for speedy approximations, which are what many decisions tend to be based on.
- eru 16y agoYes. I was more on the line of suggesting taking out your calculator, if you want to know when your investment doubles.
- jefffoster 16y agoSee http://en.wikipedia.org/wiki/Rule_of_72 http://en.wikipedia.org/wiki/Rule_of_72