A pharmacist combines the contents of a 30-g tube of a 0.5% ointment and a 90-g tube of a 1.5% ointment of the same active ingredient. What is the concentration of the mixture?

Question

Solve by applying: Altering Strength, Stock Solutions, and Alligation Calculations

Answer 1

30 g x 0.5 g/100 g = 0.15 g of active ingredient

90 g x 1.5 g/100 g = 1.35 g of active ingredient

Total mass of ointment = 30 g + 90 g = 120 g

Final concentration of active ingredient = 0.15 g + 1.35 g / 120 g (x100%) = 1.25%