Choice A is the correct answer. This models mixture problems (e.g., interest rates, concentrations).

1. Distribute: $0.1x + 10 - 0.05x \geq 15$
2. Combine: $0.05x + 10 \geq 15$
3. Subtract 10: $0.05x \geq 5$
4. Divide by 0.05: $x \geq 100$

?�� Strategic Tip:$5 \div 0.05 = 500 \div 5 = 100$.

Choice B is incorrect because it reverses the inequality direction. Choice C is incorrect because it might result from dividing 5 by 0.1. Choice D is incorrect because it combines wrong value and wrong direction.