7

Set 17: Exponential Functions

Explanation

Answer: A

An investment triples every 5 years. Which equation models the value after tt years if starting with $2,000?

A.

V(t)=2000(3)t/5V(t) = 2000(3)^{t/5}

✓ Correct
B.

V(t)=2000(3)5tV(t) = 2000(3)^{5t}

C.

V(t)=6000(t)V(t) = 6000(t)

D.

V(t)=2000(3)tV(t) = 2000(3)^t

Detailed Explanation

Choice A is correct. Choice A is the correct answer. Model the tripling pattern. 1. Growth Factor: Triples means multiply by 3. 2. Time Period: Every 5 years, so number of periods = t5\frac{t}{5}. 3. Equation: V(t)=2000(3)t/5V(t) = 2000(3)^{t/5}. 4. Verify: At t=5t=5, V=2000(3)1=6000V = 2000(3)^1 = 6000 (tripled) ✓ Strategic Tip: Exponent = elapsed timeperiod length\frac{\text{elapsed time}}{\text{period length}}. Choice B is incorrect because 35t3^{5 t} grows much too fast. Choice C is incorrect because this is linear, not exponential. Choice D is incorrect because this triples every year, not every 5 years.

Key Steps:

The correct answer is V(t)=2000(3)t/5V(t) = 2000(3)^{t/5}

Why others are wrong:
B: Choice B is incorrect and may result from a calculation error.
C: Choice C is incorrect and may result from a calculation error.
D: Choice D is incorrect and may result from a calculation error.

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