Give each cat one cup.
All cats have 1 cup now and there is one extra.
Take that extra cup and split it into 1/5s (because there is 1 cup left and 5 cats)
You should have 5 sets of 1/5s
Give each cat a set.
Each cat should now have 1 1/5 a cup.
The answer is 1 1/5 but the above should explain how.
