<P> Since p = rB * the formula for the payment reduces to, </P> <Dl> <Dd> p = (r + 1 λ n) B 0 (\ displaystyle p = \ left (r+ (\ frac (1) (\ lambda _ (n))) \ right) B_ (0)) </Dd> </Dl> <Dd> p = (r + 1 λ n) B 0 (\ displaystyle p = \ left (r+ (\ frac (1) (\ lambda _ (n))) \ right) B_ (0)) </Dd> <P> and the average interest rate over the period of the loan is </P>

Where did the concept of interest come from