Problem 24 - College Algebra

Question

With a growth rate \(k\) to double. Express each answer to the nearest whole year. Japan is growing at a rate of \(0.3 \%\) per year. How long will it take Japan to double its population?

Step-by-Step Solution

Answer

It takes Japan 231 years to double its population at a growth rate of \(0.3\%\) per year.

Step 1: Setting up the equation

Using the formula of continuous growth \(P = P_0 e^{kt}\), the equation is set up as \(2P_0 = P_0 e^{0.003t}\). Since we are looking for time taken for the population to double, \(P = 2P_0\). You can remove \(P_0\) from both sides.

Step 2: Solving the equation

The equation now simplifies to \(2 = e^{0.003t}\). To isolate the exponent, take the natural logarithm of both sides: \(ln(2) = ln(e^{0.003t})\). This simplifies to \(ln(2) = 0.003t\), as according to logarithmic rules, \(ln(e^a) = a\).

Step 3: Calculating the time

Solving for \(t\) gives the formula \(t = ln(2) / 0.003\). By calculating the value, you get \(t = 231 years\).

Key Concepts

Continuous Growth Formula

Understanding the continuous growth formula is crucial when studying population dynamics or finance. The formula, represented as P = P_0e^{kt}, is an application of exponential functions, where P is the future population or value, P_0 is the initial population or value, e is the base of the natural logarithm (approximately equal to 2.71828), k represents the growth rate, and t stands for time. This formula assumes that growth happens continuously and at a constant rate, which in real-life scenarios represents an idealized situation.

When the question concerns population doubling, the goal is to find when the future population P is twice the initial population P_0. To do this, you set P to 2P_0 in the formula and solve for t. In our example with Japan's population growth, the formula becomes 2P_0 = P_0 e^{0.003t}. After canceling out P_0 on both sides, we are left with 2 = e^{0.003t}, which is the key equation to solve for the time to double.

Natural Logarithm Calculation

To solve equations in the form C = e^{at} for t, we need to understand natural logarithms. The natural logarithm, denoted as ln, is the logarithm to the base e, where e is an irrational and transcendental constant approximately equal to 2.71828. Natural logarithms are the inverse operation of taking e to a power. Thus, ln(e^a) = a, an identity that is particularly handy in solving our continuous growth equation.

In the given problem, after setting up the equation, we take the natural logarithm of both sides: ln(2) = ln(e^{0.003t}). This utilizes the fundamental logarithmic property that allows us to move the exponent out in front: ln(e^{a}) = a. This step simplifies our equation to ln(2) = 0.003t and isolates t, making it possible to find the doubling time of the population.

Doubling Time Equation

The doubling time equation is specifically derived to determine the period it takes for a quantity to double in size at a constant growth rate. This equation comes in particularly handy when dealing with population studies, financial investments, or in any scenario where exponential growth is present. To find the doubling time, we often reorganize the continuous growth formula to isolate t, resulting in the equation t = ln(2) / k.

This is derived from our previous step where we had 2 = e^{kt}. After taking the natural logarithm of both sides and applying the rules of logarithms, we find that t is the ratio of the natural logarithm of 2, which symbolizes the 'doubling' aspect, to the growth rate k. In our example, by substituting the given growth rate of 0.3% (converted to decimal as 0.003) into the equation t = ln(2) / 0.003, we can calculate the exact time needed for Japan's population to double. By doing the math, we find the doubled population is expected in approximately 231 years.