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_18118221_1 (annual_interchanges__millions__2011_12 VARCHAR, annual_entry_exit__millions__2011_12 VARCHAR)

### Question ###
How many annual interchanges in the millions occurred in 2011-12 when the number of annual entry/exits was 36.609 million? 

### Accurate SQL ###

SELECT annual_interchanges__millions__2011_12 FROM table_18118221_1 WHERE annual_entry_exit__millions__2011_12 = "36.609"