Please help me to understand TypeError: Expected tuple, got str
#### Code Sample, a copy-pastable example if possible

```python
# Summarize data by schools
schools_group = complete_data_pd.groupby(["school_name"])
sum_students = schools_group["student_name"].value_counts()
budgets_df = schools_group["budget"].mean()
per_student = budgets_df / sum_students
math_mavens_group = complete_data_pd[complete_data_pd['math_score'] >= 70].groupby(["school_name"])
rad_readers_group = complete_data_pd[complete_data_pd['reading_score'] >= 70].groupby(["school_name"])
math_per_school = schools_group["math_score"].mean()
reading_per_school = schools_group["reading_score"].mean()
mavens_per_school = math_mavens_group.count()["student_name"] / sum_students
readers_per_school = rad_readers_group.count()["student_name"] / sum_students
rate_passing = ((mavens_per_school + readers_per_school) / 2)

# Create new dataframe
summary_df = pd.DataFrame({
                           "School Type" : type,
                          "Total Budget" : budgets_df,
                          "Budget Per Student" : per_student,
                          "Average Math Score" : math_per_school, 
                          "Average Reading Score" : reading_per_school, 
                          "% Passing Math" : mavens_per_school, 
                          "% Passing Reading" : readers_per_school, 
                            "% Overall Passing Rate" : rate_passing
                          })

```
#### Problem description

If this has been answered in an earlier issue, I couldn't translate it into anything I understand

The above code is my attempt to create a new dataframe by using a groupby object from an earlier dataframe. When I try to run the code, I get a whole lot of traceback that I do not understand, ending with the line, TypeError: Expected tuple, got str.

The error message suggests that the problem is in the line, "% Overall Passing Rate" : rate_passing; however, when I remove that line, the same error message throws, but now points to the new last line. Putting brackets around the variables did nothing. What exactly is going on here with tuples and strings?