It depends on the amount of friends there is. Without leftovers, they must all be whole numbers
18 muffins in all
For 1 friend
18/1 = 18
For 2 friends
18/2 = 9
For 3 friends
18/3 = 6
For 6 friends
18/6 = 3
For 9 friends
18/9 = 2
For 18 friends
18/18 = 1
hope this helps