A solution contains 40 mg per 5 mL. How many milligrams are in 12 mL?

• A. 8 mg
• B. 40 mg
• C. 96 mg
• D. 240 mg

Answer: (C)

This question tests understanding of concentration and proportional reasoning. If a solution has 40 mg in 5 mL, that’s 40 ÷ 5 = 8 mg per 1 mL. To find the amount in 12 mL, multiply the per-milliliter amount by 12: 8 mg/mL × 12 mL = 96 mg. Equivalently, set up a proportion: 40 mg/5 mL = x mg/12 mL, so x = 40 × 12 ÷ 5 = 96 mg. So there are 96 mg in 12 mL. The other numbers don’t fit because 8 mg is the amount per milliliter, not the total in 12 mL; 40 mg is the total in 5 mL, not 12 mL; and 240 mg would require a larger volume at the same concentration (for example, about 30 mL).