How many ml of cranberry juice is required to prepare a 25 ml 12% cranberry solution using a 20% cranberry stock solution?

To answer this question, you need to equalize the content of the cranberry for both solutions. The content could be count by multiplying the percentage with the volume of the cranberry juice. Then the calculation would be:

content1 = content2

concentration1 * volume1 = concentration2 * volume2

12% * 25 ml = 20% * volume2

volume2 = 25ml * 12% / 20% = 15ml