Set 13: Exponential Functions (Advanced)

Choice A is correct. Choice A is the correct answer. Find when charge drops below 80%. 1. Retention: Loses 5%, keeps 95% = 0.95 per day. 2. Formula: $C(t) = 100(0.95)^t$. 3. Test: - Day 4: $100(0.95)^4 \approx 81.45\%$ (above 80%) - Day 5: $100(0.95)^5 \approx 77.38\%$ (below 80%) ✓ 4. Answer: 5 days. Strategic Tip: Test successive days to find when it crosses the threshold. Choice B is incorrect because charge is still above 80% at day 4. Choice C is incorrect because charge is well above 80% at day 3. Choice D is incorrect because it drops below 80% before day 6.