Dario purchased a party size sub, and he decides to share it with 3 of his friends. So, he cuts the sub into 4 equal pieces. However, another one of his friends also showed up, and there are now 5 people in total.

Explanation:
Let's make an illustration of the shared parts first.
So, at first, Dario divided the party size into 4 parts first.
Then, here comes another friend. Dario divided each piece into 5 parts.
Based on the illustration above, each friend receives 4 pieces out of 20 cut pieces.
Answer:
The fraction of the party size sub that each person got after all the parts were shared is 4/20 or 1/5.