Well, 4 cups is equal to 1 quart. But we have 2; thus 4+4, or 4*2. We get 8, which means he made 8 cups of juice. since 2/4 is also equal to 1/2 and 1/2 is not equal to 8 his mistake is basically that he did his math wrong. It doesn't even state where he got his 4 from.. ? :) Does this help?