effective interest rate
A discount electronics store advertises the following ﬁnancing arrangement: “We don’t oﬀer you confusing interest rates. We’ll just divide your total cost by 10 and you can pay us that amount each month for a year.” The ﬁrst payment is due on the date of sale and the remaining eleven pay- ments at monthly intervals thereafter. Calculate the eﬀective annual interest rate the store’s customers are paying on their loans.
P.S.The ans is 51.2%. I don't know how to do.