Choice A is the correct answer. Find when value drops below 50%.

1. Retention: Keeps 80% each year, so $V(t) = V_0(0.8)^t$.
2. Test values:
   • Year 1: $(0.8)^1 = 0.80 = 80\%$
   • Year 2: $(0.8)^2 = 0.64 = 64\%$
   • Year 3: $(0.8)^3 = 0.512 = 51.2\%$ (still above 50%)
   • Year 4: $(0.8)^4 = 0.4096 = 40.96\%$ (below 50%) ✓
3. Answer: 4 years.

💡 Strategic Tip: Test successive years until value drops below the threshold.

Choice B is incorrect because after 3 years, value is still 51.2%. Choice C is incorrect because after 2 years, value is 64%. Choice D is incorrect because it drops below 50% before year 5.