There is 2/3 cup of pineapple juice used for every 1/3 cup of orange juice. If you have 1 cup of orange juice, that is 3 times more than 1/3 cup. So you multiply 2/3 pineapple juice and 3 to get an answer of 2 cups of pineapple juice. You can also look at it as there being a ratio of 2:1, pineapple to orange. So there is always twice the amount of pineapple juice than orange juice. So if you have 10 cups of pineapple juice, you have 5 cups of orange juice.