Choice A is the correct answer. Decrease of 50% means factor is 0.5.

1. Identify Rate: $r = 0.50$.
2. Calculate Factor: $b = 1 - 0.50 = 0.50$.
3. Equation: $y = 100(0.5)^t$.

💡 Strategic Tip: Losing 50% is the same as keeping 50%. This is also called half-life.

Choice B is incorrect because 1.5 means 50% growth. Choice D is incorrect because 0.05 means losing 95%.