Choice A is the correct answer. Let $c$ = chocolate bars and $l$ = lollipops.

System: $\begin{cases} c + l = 20 \\ 2c + 0.5l = 25 \end{cases}$

Step 1: From first equation: $l = 20 - c$

Step 2: Substitute: $2c + 0.5(20 - c) = 25$$2c + 10 - 0.5c = 25$$1.5c = 15$$c = 10$

Solution: 10 chocolate bars (and 10 lollipops)

Verification: $10 + 10 = 20$ ✓ and $2(10) + 0.5(10) = 20 + 5 = 25$ ✓

💡 Strategic Tip: Convert decimals to fractions if it helps: $0.5 = \frac{1}{2}$.

Choice B is incorrect because $2(12) + 0.5(8) = 24 + 4 = 28 \ eq 25$.

Choice C is incorrect because $2(15) + 0.5(5) = 30 + 2.5 = 32.5 \ eq 25$.

Choice D is incorrect because $2(8) + 0.5(12) = 16 + 6 = 22 \ eq 25$.