Fill Missing Scores

An analytics system collects user scores but some entries are missing. Fill each missing score with the mean of all non-null scores, rounded to 2 decimal places, and return the full DataFrame in the original row order.

Schema

df

column	type
user_id	int
score	float (nullable)

Sample Input

user_id	score
1	80.0
2	90.0
3	NaN
4	70.0

Expected Output

user_id	score
1	80.0
2	90.0
3	80.0
4	70.0

Explanation

The mean of the three non-null scores (80 + 90 + 70) / 3 = 80.0, so the NaN in row 3 is replaced with 80.0.