The ratio of pineapple juice to ginger ale is 3:4. To get from 4 cups of ginger ale to 16 cups, we multiply by four. To keep the ratio, we do the same to the amount of pineapple juice so there should be 12 cups of pineapple juice. To check our ratio, we can see that 12:16 simplifies to 3:4 when we divide by four.
Answer: 12 cups of pineapple juice
