you need to multiply 5 by 1/4 (5 cats eat 1/4 cup of cat food). then you multiply 6 by 1/5 (6 cats eat 1/5 cup of cat food). the five cats eat 5/4 cups of cat food and six cats eat 6/5 cups of cat food. then add 5/4 and 6/5 and you get 49/20 or 2 9/10.
