At 6% interest, your money takes 72/6 or 12 years to double.To double your money in 10 years, get an interest rate of 72/10 or 7.2%.If your country’s GDP grows at 3% a year, the economy doubles in 72/3 or 24 years.If your growth slips to 2%, it will double in 36 years. If growth increases to 4%, the economy doubles in 18 years. Given the speed at which technology develops, shaving years off your growth time could be very important.