First, make a percent proportion table. put 100 on the bottom right line, then put your whole which is 60, on the bottom left line. put your 20 cups of lemonade on the top left line. put an x on the top right line to indicate that there is no verified percent to use. Now, use the butterfly multiplication method. which is making a bubble from the bottom left and top right corners, and doing it the same to the top left and bottom right corners. when you have multiplied the bubbled numbers it should be 2000 divided by 60x so divide that and you should get your answer of 33.3333 ( and it keeps repeating itself forever.) Have a nice day!