Dario decides to take each one of the 4 pieces and share it equally among the 5 of them. First, he divides one piece into 5 equal parts and shares it, then the next one, and so on.
At the end of this process, Dario and his 4 friends will each have 5 portions of the original 4 pieces of cake, which means they will have 20 portions of cake in total.
Each portion will be 1/5 of a piece of cake, so Dario and his friends will have:
20 portions x 1/5 piece per portion = 4 pieces of cake
So even though Dario divided the cake into smaller portions, they still have the same amount of cake in total.