Calculating 50% Reduction in Malaria Cases Steps:

• Identify 50% lower as 2019 cases being half of 1990 cases (2019 = 0.5 × 1990).
• For each country, divide 2019 cases by 1990 cases and check if result equals 0.5.
• Country A: ratio 0.7 (30% decrease).
• Country B: ratio 0.5 (50% decrease); select B.

Why B is correct:

• Country B's 2019 cases equal exactly 50% of 1990 cases, matching the definition of 50% lower.

Why the others are wrong:

• A: 2019 cases are 70% of 1990, a 30% decrease.
• C: 2019 cases exceed 1990, an increase.
• D: 2019 cases are 25% of 1990, a 75% decrease.

Final answer: B