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At the start of 1985, the incidence of AIDS was doubling every 6 months and 40,000 cases had been reported in the United States. Assuming this trend would have continued, determine when, to the nearest tenth of a year, the number of cases would have reached 1 million.

Short Answer

Expert verified
The number of AIDS cases would have reached 1 million after approximately 2.3 years, starting from the beginning of 1985. This corresponds to around February or March of 1987.

Step by step solution

01

Identify the exponential growth formula

The exponential growth formula is \(N(t) = N_0(2)^{\frac{t}{T}}\), where \(N(t)\) is the number of cases at time t, \(N_0\) is the initial number of cases, t is time (in this case, in years), and \(T\) is the doubling time (in this case, 6 months).
02

Substitute the given values into the formula

We are given that \(N_0 = 40{,}000\) cases, \(T = 0.5\) years (since 6 months is half a year), and the desired number of cases is 1 million. We will solve the equation for time t: \(1{,}000{,}000 = 40{,}000(2)^{\frac{t}{0.5}}\).
03

Solve for t

First, divide by 40,000 to isolate the exponential term: \(25 = (2)^{\frac{t}{0.5}}\). Taking the logarithm base 2 of both sides, we have: \(\log_2{25} = \frac{t}{0.5}\). Now, multiply by 0.5 to get t alone: \(t = 0.5 \times \log_2{25}\).
04

Calculate the value of t

Use your calculator to determine the value of t: \(t = 0.5 \times \log_2{25} \approx 2.322\).
05

Interpret the result

The number of AIDS cases would have reached 1 million after approximately 2.3 years, starting from the beginning of 1985. Since we're dealing with the nearest tenth of a year, we can find the exact month as well. One-tenth of a year is 1.2 months. Therefore, the 1 million cases would have been reached around February or March of 1987.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Mathematical Modeling
Mathematical modeling is an essential technique applied in various fields to describe real-world scenarios using the language of mathematics. This process involves creating mathematical representations of systems to analyze and predict behavior. In our exercise, we use mathematical modeling to predict the progression of the AIDS epidemic. The model starts with an assumption, which sets up the initial condition of 40,000 reported AIDS cases in 1985, and the trend of these cases doubling every six months.

A powerful aspect of mathematical modeling is its ability to utilize conditions and constraints to forecast future events. By incorporating exponential growth into the model, we can estimate the future number of cases. Furthermore, mathematical models are not static; they can be refined as new data becomes available, improving their accuracy and reliability.
Logarithm Calculations
Logarithm calculations are a fundamental tool for solving equations involving exponential functions, which commonly occur in growth and decay problems. When we encounter the question of determining when the number of AIDS cases would reach a certain threshold, logarithms come into play. Firstly, it's vital to understand the logarithm property that allows us to isolate the variable of interest, in this case, the time ('t').

In the given solution, calculating the logarithm base 2 of both sides of the equation \(25 = (2)^{\frac{t}{0.5}}}\) simplifies the problem by enabling us to solve for 't'. The property exploited here is that a logarithm of a number to a specific base answers the question: 'To what power must we raise this base to obtain the number?' Using logarithms turns the process of finding the time at which an event happens from a guessing game into a straightforward calculation. As we can see from this exercise, a firm grasp of logarithms is indispensable for students working with exponential growth scenarios and interpreting data.
Exponential Functions
Exponential functions are ubiquitous in the mathematical modeling of processes that change at rates proportional to their current value. They are represented in the form \(N(t) = N_0e^{kt}\), where \(N_0\) is the initial amount, \(e\) is the base of the natural logarithm, and \(k\) is a constant that defines the growth () or decay () rate. However, in our specific example with the AIDS cases doubling every six months, our function is \(N(t) = N_0(2)^{\frac{t}{T}}}\), with 'T' being the doubling time.

Understanding exponential functions is critical because they are not linear; they do not increase by the same amount each period but rather grow by a factor. Such growth occurs in populations, investments, and, as shown in this problem, disease spread. Recognizing how to work with exponential functions, including performing transformations and interpreting parameters, is crucial for predicting the outcomes of dynamically changing systems.

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