Euler Problem 1

I've decided to do a series of posts with my solutions to the Euler problems.  They'll be tagged with "euler", and once I figure out how I'll stop them from showing up on the main page.
<pre lang="scheme">This is the first Euler Problem
(define sum
  (lambda (x) (apply + x)))
(define product
  (lambda x (apply * x)))
(define sum-1-to-n
  (lambda (x) (* (/ 1 2) x (+ x 1))))
(define (1+ x) (+ x 1))
(define (-1+ x) (- x 1))

(let
    ((smalllist '(3 5 6 9 10 12 15))
     (num15s (quotient 1000 15)))
  "(* num15s 15) -> 990, so we add the last few by hand"
  (+ (* 15
        (length smalllist)
        (sum-1-to-n (-1+ num15s)))
     (* num15s (sum smalllist))
     993 995 996 999))</pre>