Massachusetts Pharmacy Technician License Practice Test

When filling a prescription for 15g of a topical steroid cream at 12% concentration, using available 10% and 15%, how much of each is needed?

1. 5g of 10% + 10g of 15%

2. 6g of 10% + 9g of 15%

3. 9g of 10% + 6g of 15%

4. 6g of 15% + 9g of 10%

The correct answer is: 6g of 15% + 9g of 10%

To find the correct combination of the 10% and 15% topical steroid cream to achieve a final concentration of 12% in a total of 15 grams, we must use a method called the alligation method. The alligation method helps determine the proportions of two solutions of different concentrations that can be mixed to achieve a desired concentration. In this case, we have two concentrations: 10% and 15%. We want to find out how much of each is required to make 15 grams of a 12% solution. 1. **Identify the Concentrations:** - The lower concentration is 10%. - The higher concentration is 15%. - The desired concentration is 12%. 2. **Set Up the Alligation:** - Calculate the differences between the concentrations: - From the higher concentration (15%) to the desired concentration (12%): 15% - 12% = 3% - From the desired concentration (12%) to the lower concentration (10%): 12% - 10% = 2% 3. **Ratio of the Components:** - The ratio of the quantities of the 10% solution to the 15% solution will be