Final answer:
The equation for percent annual growth (natural increase) is calculated using the Rule of 70. The doubling time equation is t₂ = ln 2/ln(1 + p).
Step-by-step explanation:
The equation for percent annual growth (natural increase) is calculated using the Rule of 70. The doubling time associated with a percentage growth rate is found by dividing 70 by the percentage rate. For example, if the growth rate is 2%, the doubling time would be 70/2 = 35 years.
The equation for doubling time can be derived from the natural logarithm. It is given by t₂ = ln 2/ln(1 + p), where ln denotes the natural logarithm and p is the annual growth rate in percent. This equation provides a more accurate estimation of the doubling time.