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_76 (ratio INTEGER, similar_iso_a_size VARCHAR)

### Question ###
Which Ratio has a Similar ISO A size of a3?

### Accurate SQL ###

SELECT AVG(ratio) FROM table_name_76 WHERE similar_iso_a_size = "a3"