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One model for the number of students enrolled in U.S. public high schools as a function of time since 1986 is $$ N=0.05 t^{2}-0.42 t+12.33 $$ Here \(N\) is the enrollment in millions of students, \(t\) is the time in years since 1986 , and the model is relevant from 1986 to \(1996 .\) a. Use functional notation to express the number of students enrolled in U.S. public high schools in the year 1989 , and then calculate that value. b. Explain in practical terms what \(N(8)\) means and calculate that value. c. In what year was the enrollment the smallest?

Short Answer

Expert verified
In 1989, there were 11.52 million students. \(N(8)\) represents 1994 with 12.17 million students. The smallest enrollment was in 1990.

Step by step solution

01

Express Enrollment in 1989

Since the year 1989 is three years after 1986, set \(t = 3\) for our function. In functional notation, this is expressed as \(N(3)\). The function is given by \(N = 0.05t^2 - 0.42t + 12.33\), so substitute \(t = 3\).
02

Calculate Enrollment in 1989

Substitute \(t = 3\) into the function: \[ N(3) = 0.05(3)^2 - 0.42(3) + 12.33 \]. Calculate each term: \(3^2 = 9\), so \(0.05 \times 9 = 0.45\). Then \(-0.42 \times 3 = -1.26\). Add these to the constant 12.33: \[ N(3) = 0.45 - 1.26 + 12.33 = 11.52 \]. Thus, 11.52 million students were enrolled in 1989.
03

Interpret and Calculate N(8)

\(N(8)\) represents the number of students enrolled 8 years after 1986, which is the year 1994. Substitute \(t = 8\) into the function: \[ N(8) = 0.05(8)^2 - 0.42(8) + 12.33 \]. Calculate \(8^2 = 64\), so \(0.05 \times 64 = 3.2\). Then \(-0.42 \times 8 = -3.36\). Add these to 12.33: \[ N(8) = 3.2 - 3.36 + 12.33 = 12.17 \]. Thus, 12.17 million students were enrolled in 1994.
04

Determine Year of Smallest Enrollment

To find the smallest enrollment, calculate the function \(N\) for each year from \(t = 0\) to \(t = 10\) and find the minimum. Compute \(N(t)\) at each point and note that function calculus or plotting might show the minimum occurs at an endpoint. Calculate for \(t = 0, 1, 2, \ldots, 10\) to find the year with the lowest value.
05

Compare Values to Find Smallest Enrollment

Calculate and compare the following: \(N(0) = 12.33\), \(N(1) = 11.96\), \(N(2) = 11.69\), \(N(3) = 11.52\), \(N(4) = 11.45\), \(N(5) = 11.48\), \(N(6) = 11.61\), \(N(7) = 11.84\), \(N(8) = 12.17\), \(N(9) = 12.6\), and \(N(10) = 13.13\). The minimum value is \(N(4) = 11.45\), indicating the smallest enrollment happened 4 years after 1986, in the year 1990.

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Key Concepts

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

Exponential Functions
Exponential functions are a fundamental concept in mathematics, particularly in college algebra, and are key to describing situations where growth or decay happens at a constant percentage rate. In this exercise, the given model to describe student enrollment is a quadratic function, a specific type of polynomial function, rather than an exponential one. However, the concept is similar—both illustrate how quantities change over time. Exponential growth or decay can often model situations like population growth, radioactive decay, or interest compounding. But in our given scenario, we use a quadratic function that involves terms of a polynomial degree of two.
These polynomial functions describe various real-world phenomena where changes are not as rapid or steep as in exponential growth or decay. Here, the equation represents student enrollment over time, incorporating a quadratic term ( =t^2 ), a linear term ( =t ), and a constant. This combination reflects how changes in student enrollments are not static or linear but have depth and complexity that take into account various factors, such as socio-economic aspects, that might influence the rates of enrollment in reality.
Understanding exponential and polynomial functions becomes essential when modeling scenarios where variables exhibit non-linear behaviors over periods, allowing predictions and informed decisions.
Mathematical Modeling
Mathematical modeling is a powerful tool used in algebra and other branches of mathematics to represent real-world problems in a formal mathematical framework. By using mathematical models like the one in this exercise, we can analyze, interpret, and make predictions about real phenomena. Here, the model expresses the number of students enrolled over time, using a polynomial function.
In the context of this exercise, mathematical modeling helps students see how algebraic equations can depict real historical data (such as enrollments), allowing them to:
  • Understand trends and patterns over time.
  • Use data to predict future outcomes within a certain timeframe.
  • Test hypotheses about the numbers and see the practical consequences of their calculations.
To make models as accurate as possible, mathematicians choose functions that closely match the observed data. In the problem at hand, the variables need adjustment until the function best fits the trajectory of student numbers across the years 1986 to 1996. By engaging in mathematical modeling, students deepen their understanding of how math can interact with and elucidate real-world situations.
Functional Notation
Functional notation is an essential part of algebra that simplifies how we express and work with algebraic functions. Using functional notation helps to succinctly communicate information about how a function behaves with inputs and outputs. For instance, in the exercise, the instruction to find the student enrollment for a specific year is effectively expressed as \(N(3)\), where \(t\) represents the number of years since 1986.
When you see \(N(t)\), read it as the output of the function for the input \(t\). This notation speaks directly to:
  • Substituting values: When \(t = 3\), you substitute into the function to find specific outputs.
  • Simplifying and clarifying processes: It becomes a way to streamline communication, making it immediate and clear to specify the inputs and corresponding calculations.
Furthermore, understanding functional notation is instrumental in exploring relationships between variables, calculating specific values, and making algebra a more transparent, universal succinct language across different contexts. In our exercise, using \(N(t)\) allows for straightforward calculations to understand how enrollment fluctuated during 1986 to 1996.

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Most popular questions from this chapter

Astronauts looking at Earth from a spacecraft can see only a portion of the surface. 10 See Figure \(2.59\) on the next page. The fraction \(F\) of the surface of Earth that is visible at a height \(h\), in kilometers, above the surface is given by the formula $$ F=\frac{0.5 h}{R+h} . $$ Here \(R\) is the radius of Earth, about 6380 kilometers. (For comparison, 1 kilometer is about \(0.62\) mile, and the moon is about 380,000 kilometers from Earth.) a. Make a graph of \(F\) versus \(h\) covering heights up to 100,000 kilometers. b. A value of \(F\) equal to \(0.25\) means that \(25 \%\), or one-quarter, of Earth's surface is visible. At what height is this fraction visible? c. During one flight of a space shuttle, astronauts performed an extravehicular activity at a height of 280 kilometers. What fraction of the surface of Earth is visible at that height? d. Is the graph of \(F\) concave up or concave down? Explain your answer in practical terms. e. Determine the limiting value for \(F\) as the height \(h\) gets larger. Explain your answer in practical terms.

The background for this exercise can be found in Exercises 11, 12,13, and 14 in Section 1.4. A manufacturer of widgets has fixed costs of \(\$ 600\) per month, and the variable cost is \(\$ 60\) per thousand widgets (so it costs \(\$ 60\) to produce a thousand widgets). Let \(N\) be the number, in thousands, of widgets produced in a month. a. Find a formula for the manufacturer's total cost \(C\) as a function of \(N\). b. The highest price \(p\), in dollars per thousand widgets, at which \(N\) can be sold is given by the formula \(p=70-0.03 N\). Using this, find a formula for the total revenue \(R\) as a function of \(N\). c. Use your answers to parts a and \(b\) to find a formula for the profit \(P\) of this manufacturer as a function of \(N\). d. Use your formula from part c to determine the production level at which profit is maximized if the manufacturer can produce at most 300 thousand widgets in a month.

If you borrow \(\$ 120,000\) at an APR of \(6 \%\) in order to buy a home, and if the lending institution compounds interest continuously, then your monthly payment \(M=M(Y)\), in dollars, depends on the number of years \(Y\) you take to pay off the loan. The relationship is given by $$ M=\frac{120000\left(e^{0.005}-1\right)}{1-e^{-0.06 Y}}. $$ a. Make a graph of \(M\) versus \(Y\). In choosing a graphing window, you should note that a home mortgage rarely extends beyond 30 years. b. Express in functional notation your monthly payment if you pay off the loan in 20 years, and then use the graph to find that value. c. Use the graph to find your monthly payment if you pay off the loan in 30 years. d. From part b to part \(\mathrm{c}\) of this problem, you increased the debt period by \(50 \%\). Did this decrease your monthly payment by \(50 \%\) ? e. Is the graph concave up or concave down? Explain your answer in practical terms. f. Calculate the average decrease per year in your monthly payment from a loan period of 25 to a loan period of 30 years.

The farm population has declined dramatically in the years since World War II, and with that decline, rural school districts have been faced with consolidating in order to be economically efficient. One researcher studied data from the early 1960 s on expenditures for high schools ranging from 150 to 2400 in enrollment. \({ }^{34}\) He considered the cost per pupil as a function of the number of pupils enrolled in the high school, and he found the approximate formula $$ C=743-0.402 n+0.00012 n^{2} $$ where \(n\) is the number of pupils enrolled and \(C\) is the cost, in dollars, per pupil. a. Make a graph of \(C\) versus \(n\). b. What enrollment size gives a minimum per-pupil cost? c. If a high school had an enrollment of 1200 , how much in per-pupil cost would be saved by increasing enrollment to the optimal size found in part b?

The number of species of a given taxonomic group within a given habitat (often an island) is a function of the area of the habitat. For islands in the West Indies, the formula $$ S(A)=3 A^{0.3} $$ approximates the number \(S\) of species of amphibians and reptiles on an island in terms of the island area \(A\) in square miles. This is an example of a species-area relation. a. Make a table giving the value of \(S\) for islands ranging in area from 4000 to 40,000 square miles. b. Explain in practical terms what \(S(4000)\) means and calculate that value. c. Use functional notation to express the number of species on an island whose area is 8000 square miles, and then calculate that value. d. Would you expect a graph of \(S\) to be concave up or concave down?

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