Set 7: Exponential Functions

Choice A is correct. Choice A is the correct answer. Find when the investment doubles. 1. Target: Double means $A = 2 \times 15000 = 30000$. 2. Equation: $30000= 15000(1.07)^t$, so $(1.07)^t = 2$. 3. Estimate: Test values: - $t=10$: $(1.07)^{10} \approx 1.967$ (close to 2) - $t=11$: $(1.07)^{11} \approx 2.105$ (over 2) 4. Answer: About 10-11 years, so "About 10 years". Strategic Tip: Rule of 72: doubling time ≈ $\frac{72}{7} \approx 10$ years. Choice B is incorrect because doubling happens sooner. Choice C is incorrect because this is the interest rate, not doubling time. Choice D is incorrect because doubling occurs much earlier.