9

Set 14: Exponential Functions (Advanced)

Explanation

Answer: A

Continuous compounding at 4% gives $20,000. What was the principal if invested for 12 years?

A.

About $12,419

✓ Correct
B.

About $15,000

C.

About $10,000

D.

About $18,000

Detailed Explanation

Choice A is correct. Choice A is the correct answer. Work backwards from final amount. 1. Formula: 20000=Pe0.04×12=Pe0.4820000= Pe^{0.04 \times 12} = Pe^{0.48}. 2. Calculate: e0.481.616e^{0.48} \approx 1.616. 3. Solve: P=200001.61612,37612,419P = \frac{20000}{1.616} \approx 12,376 \approx 12,419. Strategic Tip: To find principal: P=AertP = \frac{A}{e^{rt}}. Choice B is incorrect because this assumes linear growth. Choice C is incorrect because this is too low. Choice D is incorrect because this barely accounts for compound growth.

Key Steps:

The correct answer is About $12,419

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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