Change in Linear and Exponential Functions

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AP Precalculus › Change in Linear and Exponential Functions

Questions 1 - 10
1

A car is worth $V_0=$24{,}000$. Linear depreciation: $V_L(t)=24{,}000-1{,}800t$, where $t$ is years and $$1{,}800$/year is lost. Exponential depreciation: $V_E(t)=24{,}000(0.90)^t$, where value drops 10% per year. Values are in dollars. Linear change subtracts the same amount yearly, while exponential change multiplies by the same factor yearly. In the context of this scenario, which model predicts a greater decrease after 3 years?

Both models, because they start at the same initial value.

Neither model, because depreciation cannot be modeled with functions.

Exponential model, because 10% of the current value compounds each year.

Linear model, because a constant percent always decreases more.

Explanation

This question tests AP Precalculus understanding of changes in linear and exponential functions. Linear functions change at a constant rate, represented by a straight line, while exponential functions change at a rate proportional to their current value, creating a curve. In the given scenario, we need to compare the depreciation after 3 years: linear loses $1,800×3=$5,400, while exponential retains 90% each year, resulting in $24,000×(0.90)³=$17,496, a loss of $6,504. Choice B is correct because the exponential model predicts a greater decrease ($6,504) compared to the linear model ($5,400) after 3 years. Choice A is incorrect because it makes the false claim that constant percent always decreases more, which depends on the specific values and time frame. Encourage students to calculate actual values at specific time points to compare models. Emphasize that exponential decay can exceed linear decay when the percentage is significant enough.

2

A car is purchased for $V_0=$30{,}000$. Linear depreciation: $V_L(t)=30{,}000-2{,}500t$, where $t$ is years and $$2{,}500$/year is lost. Exponential depreciation: $V_E(t)=30{,}000(0.88)^t$, where value drops 12% per year. Values are in dollars. Linear change subtracts the same dollar amount yearly, while exponential change subtracts a percent of the current value yearly. Based on the scenario described, which function best describes the change in the exponential depreciation model?

$V(t)=30{,}000-2{,}500t$

$V(t)=30{,}000(1.12)^t$

$V(t)=30{,}000(0.88)^t$

$V(t)=2{,}500(0.88)^t$

Explanation

This question tests AP Precalculus understanding of changes in linear and exponential functions. Linear functions change at a constant rate, represented by a straight line, while exponential functions change at a rate proportional to their current value, creating a curve. In the given scenario, the exponential depreciation model loses 12% of value each year, which means multiplying by (1-0.12)=0.88 annually. Choice B is correct because V(t)=30,000(0.88)^t represents starting with $30,000 and retaining 88% (losing 12%) of the value each year. Choice D is incorrect because it uses 1.12, which would represent 12% growth rather than 12% depreciation. Encourage students to recognize that depreciation by x% means multiplying by (1-x/100). Use car value examples to demonstrate how percentage-based depreciation creates exponential decay.

3

A town has $P_0=50{,}000$ people. Linear model: $P_L(t)=50{,}000+800t$, where $t$ is years and 800 people/year is constant. Exponential model: $P_E(t)=50{,}000(1.016)^t$, where 1.6% per year compounds. Both models measure population in people. The linear change adds the same number each year, while the exponential change adds a percentage of the current population. Using the information provided, how does the rate of change differ between the linear and exponential models?

Linear increases by 1.6% each year; exponential adds 800 people/year.

Both models increase by a constant percent each year.

Linear adds 800 people/year; exponential increases by 1.6% of the current population each year.

Both models increase by 800 people each year.

Explanation

This question tests AP Precalculus understanding of changes in linear and exponential functions. Linear functions change at a constant rate, represented by a straight line, while exponential functions change at a rate proportional to their current value, creating a curve. In the given scenario, the linear model adds 800 people each year (constant amount), while the exponential model grows by 1.6% of the current population annually (constant percentage). Choice B is correct because it accurately identifies that linear adds a fixed number (800 people/year) while exponential increases by a fixed percentage (1.6%) of the current population. Choice A is incorrect because it claims both models add 800 people yearly, missing that exponential growth depends on the current population size. Encourage students to identify whether the rate of change is a constant amount (linear) or constant percentage (exponential). Use population growth examples to illustrate how exponential growth accelerates over time as the base increases.

4

A town begins with $P_0=60{,}000$ people. Linear model: $P_L(t)=60{,}000+900t$, where $t$ is years and 900 people/year is constant. Exponential model: $P_E(t)=60{,}000(1.012)^t$, where 1.2% per year compounds. Population is measured in people. Linear change is additive and constant, while exponential change is multiplicative and depends on current size. Based on the scenario described, what assumptions are made in the linear model vs the exponential model?

Linear assumes the same number is added yearly; exponential assumes the same percent is applied yearly.

Linear assumes the same percent is applied yearly; exponential assumes the same number is added yearly.

Both assume the population change is unrelated to time.

Both assume the population decreases each year by a constant amount.

Explanation

This question tests AP Precalculus understanding of changes in linear and exponential functions. Linear functions change at a constant rate, represented by a straight line, while exponential functions change at a rate proportional to their current value, creating a curve. In the given scenario, the linear model assumes a constant addition of 900 people yearly, while the exponential model assumes growth by 1.2% of the current population annually. Choice A is correct because it accurately states that linear assumes the same number (900) is added yearly while exponential assumes the same percent (1.2%) is applied yearly. Choice B is incorrect because it reverses these assumptions, confusing which model uses absolute versus relative change. Encourage students to identify the fundamental difference: linear models assume change independent of current size, while exponential models assume change proportional to current size. Use population dynamics to illustrate why exponential models often better represent natural growth.

5

A lab culture begins with $N_0=5{,}000$ bacteria. Linear model: $N_L(t)=5000+300t$, where $t$ is hours and 300 bacteria/hour is constant. Exponential model: $N_E(t)=5000(1.06)^t$, where 6% per hour compounds. Counts are in bacteria. Linear growth adds a fixed number, while exponential growth scales by a fixed percent. Using the information provided, what assumptions are made in the linear model vs the exponential model?

Both assume the increase per hour is proportional to time only.

Linear assumes a constant increase; exponential assumes a constant percent increase.

Both assume the culture decreases by the same amount each hour.

Linear assumes a constant percent increase; exponential assumes a constant increase.

Explanation

This question tests AP Precalculus understanding of changes in linear and exponential functions. Linear functions change at a constant rate, represented by a straight line, while exponential functions change at a rate proportional to their current value, creating a curve. In the given scenario, the linear model assumes bacteria increase by a fixed number (300) each hour, while the exponential model assumes bacteria increase by a fixed percentage (6%) of the current population. Choice A is correct because it accurately states that linear assumes constant increase (300 bacteria/hour) while exponential assumes constant percent increase (6% per hour). Choice B is incorrect because it reverses the assumptions, confusing which model uses constant amounts versus constant percentages. Encourage students to identify the key difference: linear adds the same amount regardless of current size, while exponential adds more as the population grows. Use biological growth contexts to illustrate why exponential models often better represent population dynamics.

6

A town begins with $P_0=48{,}000$ people at $t=0$ years. One plan adds $1{,}200$ people/year: $P_L(t)=48{,}000+1200t$. Another plan grows by $2.5%$ yearly: $P_E(t)=48{,}000(1.025)^t$. Variables: $t$ in years, $P$ in people. The linear model’s increase stays constant, while the exponential model’s increase rises as $P$ rises. Based on the scenario described, which model predicts a greater change after 20 years?

Neither model, because population cannot be measured in people.

Exponential model, because the yearly increase becomes larger as the population base grows.

Linear model, because constant addition always beats percent growth over long times.

Both models, because 2.5% of 48,000 equals 1,200 every year.

Explanation

This question tests AP Precalculus understanding of changes in linear and exponential functions. Linear functions change at a constant rate, represented by a straight line, while exponential functions change at a rate proportional to their current value, creating a curve. The linear model adds exactly 1,200 people per year, while the exponential model multiplies the population by 1.025 each year, meaning the actual number added increases as the population grows. Choice B is correct because after 20 years, the exponential model yields $48,000(1.025)^{20} ≈ 78,663$ (change of 30,663), while the linear model yields $48,000 + 1,200(20) = 72,000$ (change of 24,000). Choice C is incorrect because it assumes 2.5% of 48,000 remains constant, failing to recognize that in exponential growth, the base amount changes each year. Students should understand that exponential growth compounds, making the yearly increase larger over time. Use long-term projections to demonstrate how exponential models eventually dominate linear ones.

7

A town has $P_0=20{,}000$ residents at $t=0$ years. A linear model adds $600$ residents/year: $P_L(t)=20{,}000+600t$. An exponential model grows by $3%$ per year: $P_E(t)=20{,}000(1.03)^t$. Variables: $t$ in years, $P$ in residents. The linear rate of change is constant, while the exponential rate increases as the population grows. Using the information provided, how does the rate of change differ between the linear and exponential models?

Linear adds 3% each year; exponential adds 600 residents each year.

Linear adds 600 residents each year; exponential adds a constant 3% of the current population each year.

Both models add the same number of residents each year because they start at 20,000.

Exponential adds a constant number each year; linear adds an increasing percent each year.

Explanation

This question tests AP Precalculus understanding of changes in linear and exponential functions. Linear functions change at a constant rate, represented by a straight line, while exponential functions change at a rate proportional to their current value, creating a curve. In the given scenario, the linear model adds exactly 600 residents each year regardless of population size, while the exponential model adds 3% of the current population, meaning the actual number added increases as the population grows. Choice A is correct because it accurately identifies that linear adds a fixed 600 residents annually while exponential adds 3% of the current population each year. Choice B is incorrect because it reverses the models, suggesting linear uses percentage growth when it actually uses constant addition. Encourage students to identify whether the rate of change is constant in absolute terms (linear) or proportional to the current value (exponential). Use population growth examples to show how exponential models compound while linear models maintain steady increases.

8

A car is worth $V_0=$24{,}000$ at purchase ($t=0$ years). A linear depreciation model subtracts $$2{,}000$ per year: $V_L(t)=24{,}000-2000t$. An exponential depreciation model loses $12%$ per year: $V_E(t)=24{,}000(0.88)^t$. Variables: $t$ in years, $V$ in dollars. Linear change is a constant dollar drop, while exponential change is a constant percent drop. Based on the scenario described, which function best describes the change in value if the car loses the same percent each year?

$V_E(t)=24{,}000(1.12)^t$, because depreciation means the factor is greater than 1.

$V_E(t)=24{,}000(0.88)^t$, because the value is multiplied by the same factor each year.

$V_L(t)=24{,}000-2000t$, because linear models always fit depreciation best.

$V_L(t)=24{,}000-2000t$, because subtracting is always percent loss.

Explanation

This question tests AP Precalculus understanding of changes in linear and exponential functions. Linear functions change at a constant rate, represented by a straight line, while exponential functions change at a rate proportional to their current value, creating a curve. The scenario describes a car that loses the same percent of its value each year, which is characteristic of exponential decay where the value is multiplied by a constant factor less than 1. Choice B is correct because $V_E(t)=24,000(0.88)^t$ represents losing 12% each year (keeping 88%), which matches the constant percent loss described in the question. Choice D is incorrect because it uses a factor greater than 1 (1.12), which would represent growth rather than depreciation. Help students recognize that exponential decay uses factors between 0 and 1, while growth uses factors greater than 1. Practice converting between percent decrease and decay factors (100% - 12% = 88% = 0.88).

9

An investment begins at $A_0=$10{,}000$ when $t=0$ years. A linear return model adds $$600$/year: $A_L(t)=10{,}000+600t$. A compound model grows by $5%$/year: $A_E(t)=10{,}000(1.05)^t$. Variables: $t$ in years and $A$ in dollars. Linear growth has a constant dollar rate, while exponential growth has a constant percent rate. Based on the scenario described, how does the rate of change differ between the linear and exponential models?

Both have constant rates because both are functions of time.

Linear has a constant $\$600$/year increase; exponential has a constant 5% increase on the current balance.

Linear has a constant 5% increase; exponential has a constant $\$600$/year increase.

Exponential has a constant dollar increase; linear has an increasing percent increase.

Explanation

This question tests AP Precalculus understanding of changes in linear and exponential functions. Linear functions change at a constant rate, represented by a straight line, while exponential functions change at a rate proportional to their current value, creating a curve. The linear model adds exactly $600 each year regardless of the account balance, representing a constant dollar rate of change, while the exponential model multiplies the balance by 1.05 each year, representing a constant 5% rate of change. Choice A is correct because it accurately identifies that linear has a constant $600/year increase while exponential has a constant 5% increase on the current balance. Choice B is incorrect because it reverses these characteristics, suggesting linear uses percentage growth when it actually uses constant dollar addition. Help students distinguish between absolute change (dollars per year) and relative change (percent per year). Use investment examples to show how compound interest creates increasing dollar gains while maintaining a constant percentage rate.

10

An investment starts at $V_0=$2{,}000$. Linear plan: $V_L(t)=2000+120t$, where $t$ is years and $$120$/year is added. Compound plan: $V_E(t)=2000(1.05)^t$, where 5% per year compounds. Values are in dollars. Linear growth changes by a constant amount, while exponential growth changes by a constant percent. Based on the scenario described, which function best describes the change in the compound plan’s value?

$V(t)=120(1.05)^t$

$V(t)=2000-120t$

$V(t)=2000(1.05)^t$

$V(t)=2000+120t$

Explanation

This question tests AP Precalculus understanding of changes in linear and exponential functions. Linear functions change at a constant rate, represented by a straight line, while exponential functions change at a rate proportional to their current value, creating a curve. In the given scenario, the compound plan grows by 5% annually, which means multiplying the current value by 1.05 each year, illustrating exponential growth. Choice B is correct because V(t)=2000(1.05)^t represents starting with $2,000 and multiplying by 1.05 each year, which models 5% compound growth. Choice A is incorrect because it represents linear growth (adding $120 yearly) rather than the compound growth described. Encourage students to recognize that compound interest means multiplying by (1 + rate) each period. Use financial contexts to demonstrate how exponential models capture percentage-based growth.

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