The following formula is used to calculate a population size after a certain number of years. This formula is most helpful for populations or quantities that are experiencing exponential growth. Doubling time. P=population in millions. Question 1: Suppose that the population of a certain country grows at an annual rate of 4%. Solutions. Implicit in this definition is the fact that, no matter when you start measuring, the population will always take the same amount of time to double. At that point rt = ln 2 = 0.69 If one knows the growth rate as a decimal fraction, then the doubling time t2 = 0.69 / r. By how much will it grow in 3 days?' Doubling Time Formula. As stated earlier, another approach to the doubling time formula that could be used with this example would be to calculate the annual percentage yield, or effective annual rate, and use it as r.The annual percentage yield on 6% compounded monthly would be 6.168%. How much of a 100 gram sample will remain after 15,000 years? Dependency Ratio. Global pop Growth Rate: Sample 1. An example of a half-life formula word problem is the following: 'The half-life of Carbon-14 is 5730 years. Solved Examples Using Exponential Growth Formula. P 0 = initial amount at time t = 0; r = the growth rate; e = Eulerâs number = 2.71828 (approx) Also Check: Exponential Function Formula. This doubling time â¦ Doubling time is referred to the time period required to double the value or size of investment, population, inflation etc and is calculated by dividing the log of 2 by the product of number of compounding per year and the natural log of one plus the rate of periodic return. A special case is the doubling time, which is the time when N(t)/N(0) = 2, that is the quantity has doubled from its initial value. The doubling time of a population exhibiting exponential growth is the time required for a population to double. DT=doubling time in years. Doubling time is more commonly known as the rule of 70. After solving, the doubling time formula shows that Jacques would double his money within 138.98 months, or 11.58 years. Population Doubling time by Nation FR=fertility rate (live births/female). 1.4 = = 50 Years. The doubling time is the amount of time that it takes for a quantity of something to double in size. x(t) = x 0 × (1 + r) t. Where x(t) is the final population after time t; x 0 is the initial population; r is the rate of growth Calculating Population Growth Rate and Doubling Time. That period of 45 years is known as. Population Growth Formula. When the world's population reached 6 billion in 1995, it was forecast that at a steady rate of growth the population would reach 12 billion in approximately 45 years. The Doubling time formula is used in finance to calculate the length of time needed to double an investment or money in an interest-bearing account. 50 years 2 â¦ An example of a doubling time formula word problem is the following: 'A population of bacteria doubles every 6 hours. Doubling time (in years) 70. r = 70. As per the formula, to calculate doubling time just divide constant growth rate by 100 and add it with 1 and find the log of â¦ Doubling time. Round to the hundredth.'