You need to prepare 500 mL of an 8% salicylic acid in paraffin ointment. You have 3% and 15% salicylic acid paraffin ointments available. How much of the 3% ointment is required?

Question: You need to prepare 500 mL of an 8% salicylic acid in paraffin ointment. You have 3% and 15% salicylic acid paraffin ointments available. How much of the 3% ointment is required?

Answer options:

• 167 mL
• 208 mL
• 292 mL ✅ 333 mL

Correct answer: 333 mL

Explanation: Using alligation: (Desired concentration - Lower concentration) / (Higher concentration - Lower concentration) = Ratio of lower concentration product. (8% - 3%) / (15% - 3%) = 5 / 12. This means for every 12 parts total, 5 parts come from the 15% ointment, and 7 parts come from the 3% ointment. Since we need 500 mL total, the amount of 3% ointment needed is (7/12) * 500 mL = 291.67 mL.