比如通货膨胀率为3.5%，用70除以3.5 = 20年。如果是$100，20年后会貶值为$50。
Rule of 70 to calculate the impact of inflation, which measures how many years it takes for your money's buying power to half.
If the inflation rate is 3.5%, it takes about 70/3,5 = 20 years for $100 to become $50.
2 ways to protect yourself against inflation:
1) Working harder to increase your income
2) Make your money work harder for you