How is exponential population growth expressed mathematically?

Exponential population growth is typically expressed in the form of a mathematical model where the quantity grows at a rate proportional to its current value. The most common form of this expression is:

P = A(b)^t

In this equation, P represents the population at time t, A is the initial population size, b is the growth factor, and t is the time elapsed. The growth factor b is usually greater than 1 for exponential growth, indicating that the population is increasing.

Option B, P = A(1 + r)^t, actually represents situations where a population grows by a fixed percentage rate r over time. This is often used in contexts of compound interest, but it is not the classic formulation for pure exponential growth in terms of a base b.

The choice P = A(b)^t emphasizes continuous growth, while 1 + r is more indicative of growth that occurs at discrete intervals. Hence, P = A(b)^t is the correct representation of exponential population growth, as it indicates that the population increases repeatedly by multiplying with a factor b over time, leading to a rapid increase characteristic of exponential growth.