IIT mains paper is simply AIEEE for the year 2013 and IIT advance is actually "IIT-JEE" for the year 2013.So,you should surely apply for both the exams, as you may be elligible for IIT advance exam as per your performance in JEE-mains.So,atleast try to get a minimum " AI-rank" within 70000,in order to remain in a very safe position in these exams. 
						

							
Dear Trupt Parkar,
Actually there are two Exams in this year''s IIT-JEE. IIT-JEE 2013 will have a IIT-JEE Main Paper which is like a qualifying exam for the IIT-JEE Advanced Paper. 
For Selection into the NIT''s it is enough to give just the IIT-JEE(Mains) but if you are aiming for an IIT then you must give the IIT-JEE Advanced Paper which can only be given if you clear the Main paper. 
To write the IIT-JEE Main paper you must be within the Top 20 percent of students in the Board Exams of your state in that Year. The Board exams carry a weightage of 40% and the score of IIT-JEE Mains carry a weightage of 60% and both determine your eligibilty to join a NIT and for qualifying for the IIT-JEE Advanced Paper.
 

Hope this helped you immensely..!!
All the Very Best & Good Luck to you ...!
 
Best Regards,
AskIITians Expert,
Godfrey Classic Prince
IIT-M
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