Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_23 ( number_of_languages INTEGER, frequency VARCHAR, publisher VARCHAR )

### Question ###
What is the mean number of languages for the monthly frequency when the publisher is the hearst corporation?

### Accurate SQL ###

SELECT AVG(number_of_languages) FROM table_name_23 WHERE frequency = "monthly" AND publisher = "hearst corporation"