SAT Β· Exponential Functions

Master Exponential
Growth & Decay

20 carefully crafted questions β€” from foundations to SAT-level traps. Learn the patterns, beat the test.

20
Questions
3
Difficulty Levels
∞
Retries
Memory Points
🧠 Cheat Sheet β€” Memorize These First
Ultra-compact anchor words to help you explain and recall each concept instantly.
ANCHOR-01 Β· GROW

Growth Formula

When something increases by a fixed percent per period, use exponential growth.

$$P(t) = P_0 \cdot b^t \quad b > 1$$
ANCHOR-02 · RATE→BASE

Rate β†’ Base Conversion

"Increases by r%" β†’ base = 1 + r/100
"Decreases by r%" β†’ base = 1 βˆ’ r/100

$$+4\% \Rightarrow b = 1.04$$
ANCHOR-03 Β· SCALE

Period Scaling Trick

If the exponent is t/(n/12), the period is n months β€” not years.

$$\left(\frac{6}{4}\right)t = \frac{t}{2/3} \Rightarrow 8\text{ months}$$
ANCHOR-04 Β· DECAY

Exponential Decay

Half-life, depreciation, cooling. Base is between 0 and 1.

$$P(t) = P_0 \cdot (0.5)^{t/h}$$
ANCHOR-05 Β· TRAP

Common SAT Traps

The exponent controls the period, not the rate. Read the exponent carefully before answering!

$$b^{(6/4)t} \neq b^{1.5t}\text{ per year}$$
ANCHOR-06 Β· UNITS

Unit Conversion Rule

Convert the exponent's unit to match the question's unit. Months ↔ Years: multiply or divide by 12.

$$n \text{ months} = \frac{n}{12} \text{ years}$$
Quiz Time
20 Questions Β· Select & Check
Choose an answer β€” instant feedback with explanations for wrong answers.
Q 01 / 20 Easy
Which of the following best describes an exponential function?
Q 02 / 20Easy
A population of bacteria doubles every hour. If the initial count is 500, which function models the population after $t$ hours?
Q 03 / 20Easy
If a savings account grows at 5% per year, what is the base of the exponential function?
Q 04 / 20Easy
Evaluate: $f(x) = 3 \cdot 2^x$ at $x = 4$.
Q 05 / 20Easy
A car's value decreases by 15% each year. If the original price is $20,000, which function models the car's value $V$ after $t$ years?
Q 06 / 20Medium
The function below models a city's population in thousands, $t$ years after 2003:
$$P(t) = 260(1.04)^{\left(\frac{6}{4}\right)t}$$
According to this model, the population increases by 4% every $n$ months. What is $n$?
ANCHOR-03 SCALE: The exponent $\frac{6}{4} \cdot t$ means "how many periods of $\frac{4}{6}$ years" have passed. Convert years β†’ months.
Q 07 / 20Medium
The function $P(t) = 180(1.06)^{2t}$ models a population (in thousands). How often does it grow by 6%?
Q 08 / 20Medium
Which of the following is equivalent to $2^{3t}$?
Q 09 / 20Medium
A town's population is modeled by $P(t) = 5000 \cdot (1.03)^{t/5}$. What does the "5" in the exponent tell you?
Q 10 / 20Medium
A radioactive substance has a half-life of 8 years. Starting with 200 grams, which function models the remaining mass $M$ after $t$ years?
Q 11 / 20Medium
The function $f(x) = 400 \cdot (0.92)^x$ models the population of a species after $x$ years. What is the annual percent decrease?
Q 12 / 20Medium
A function is given as $f(t) = 120 \cdot (1.05)^{t/12}$. What is the monthly growth rate?
Q 13 / 20Hard
The function $P(t) = 500(1.02)^{(4/3)t}$ models a population where $t$ is in years. The population grows by 2% every $n$ months. Find $n$.
ANCHOR-03 SCALE: The period is $\frac{3}{4}$ of a year. Convert: $\frac{3}{4} \times 12 = ?$ months.
Q 14 / 20Hard
Which expression is equivalent to $(1.04)^{(6/4)t}$? (Think: rewrite in the form $b^t$)
Q 15 / 20Hard
Two functions are given:

$f(t) = 100 \cdot (1.1)^t \quad$ and $\quad g(t) = 100 \cdot (1.1)^{2t}$

Compared to $f$, the function $g$ reaches $200$ (double) in:
Q 16 / 20Hard
The population model is $P(t) = 1000 \cdot b^t$ where $P(3) = 1728$. What is the value of $b$?
Q 17 / 20Hard
A quantity grows by 20% every 3 months. Which function correctly models this, where $t$ is in years?
Q 18 / 20Hard
If $f(x) = a \cdot b^x$ passes through $(0, 4)$ and $(2, 36)$, what are the values of $a$ and $b$?
Q 19 / 20Hard
The function $P(t) = 260(1.04)^{(6/4)t}$ is rewritten as $P(t) = 260 \cdot k^t$. What is the approximate value of $k$?
ANCHOR-05 TRAP: Compute $(1.04)^{6/4} = (1.04)^{1.5}$ β€” this is the annual multiplier.
Q 20 / 20Hard
A model is $P(t) = 400(1.03)^{(12/3)t}$ where $t$ is in years. By what percent does the population increase every 3 months? And what is the equivalent annual growth rate?
$$P(t) = 400(1.03)^{4t}$$
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