(define imprime-na-base
  (lambda (num base)
    (cond ((< num base) (display num))
          (else
           (imprime-na-base (quotient num base) base)
           (display (remainder num base))))))

(define decimal->outra
  (lambda (num)
    (if (< num 10)
        (display num)
        (cond ((< num 20)
               (case num
                 ((10)
                  (display "a"))
                 ((11)
                  (display "b"))
                 ((12)
                  (display "c"))
                 ((13)
                  (display "d"))
                 ((14)
                  (display "e"))
                 ((15)
                  (display "f"))
                 ((16)
                  (display "g"))
                 ((17)
                  (display "h"))
                 ((18)
                  (display "i"))
                 ((19)
                  (display "j"))))
              (else
               (display "?"))))))

(define imprime-ate-base-20
  (lambda (num base)
    (cond ((< num base) (decimal->outra num))
          (else
           (imprime-ate-base-20 (quotient num base) base)
           (decimal->outra (remainder num base))))))

(define interest-rate
  (lambda (n)
    (case n ((1)
             0.02)
      ((2)
       0.024)
      ((3)
       0.032)
      (else
       0.038))))

(define accumulate
  (lambda (amount n-years)
    (if (or (< amount 0) (<= n-years 0))
        (display "invalid parameter(s)")
        (accumulate-aux amount n-years 1))))

(define accumulate-aux
  (lambda (amount n-years year)
    (if (not (> year n-years))
        (begin
          (let ((interest (interest-rate year)))
            (accumulate-aux (* amount (+ 1 interest)) n-years (add1 year))))
        (/ (round (* amount 100)) 100))))