4

Set 6: Exponential Functions (Advanced)

Explanation

Answer: A

An investment of $15,000 is compounded continuously at 6.5% annual rate. How long until it reaches $30,000?

A.

About 10.7 years

✓ Correct
B.

About 15 years

C.

About 8 years

D.

About 12 years

Detailed Explanation

Choice A is correct. Choice A is the correct answer. Solve for tt using continuous compounding. 1. Formula: 30000=15000e0.065t30000= 15000 e^{0.065 t}. 2. Divide: 2=e0.065t2= e^{0.065 t}. 3. Natural log: ln(2)=0.065t\ln(2) = 0.065 t. 4. Solve: t=ln(2)0.065=0.6930.06510.6610.7t = \frac{\ln(2)}{0.065} = \frac{0.693}{0.065} \approx 10.66 \approx 10.7 years. Strategic Tip: Doubling time for continuous growth: t=ln(2)rt = \frac{\ln(2)}{r}. Choice B is incorrect because this is too long. Choice C is incorrect because this is too short. Choice D is incorrect because this doesn't match the calculation.

Key Steps:

The correct answer is About 10.7 years

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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