'Why is this creating a table of NaNs?

I am analyzing test data and school budget data using pandas in jupyter notebook. This calculation is passing what appears to be a dataframe with a NaN in every field. Based on the calculation, it seems that it should be a list of schools with a percentage ov students passing BOTH reading and math. The per_overall_passing variable was calculated in the previous cell. However, it is producing a dataframe as well. Should this not be a series or a list? I've tried .set_index with the per_overall_passing dataframe. This returns 'method' object is not subscriptable error.

# Calculate the overall passing percentage.
per_overall_passing_percentage = per_overall_passing / per_school_counts * 100
per_overall_passing_percentage


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