A car dealer offers payments of $522.59 per month for 48 months on a $25,000 car after making a $4,000 down payment. What is the loan's APR? I did this : N= 48, PV=21000,FV=0,PMT = -522.59 , APR =9%

BUT

My question is: if we pay 522.59/month for 48 months that's = 522.59*48= 25084.32 So, interest = 25084.32 - 21000 = 4084.32 Here is the confusion: As far as I know.. Interest rate =( intrest amount/ original amount )* 100 =( 4084.32 / 21000 ) * 100 = 19.4491% !! not 9% why the two rates are not the same?