#| BEGIN (Write your solution here) |#
(define (make-segment p1 p2)
  (cons p1 p2))

(define (start-segment s)
  (car s))

(define (end-segment s)
  (cdr s))

(define (make-point x y)
  (cons x y))

(define (x-point p)
  (car p))

(define (y-point p)
  (cdr p))

(define (midpoint-segment s)
  (let ((x1 (x-point (start-segment s)))
        (x2 (x-point (end-segment s)))
        (y1 (y-point (start-segment s)))
        (y2 (y-point (end-segment s))))
    (make-point (avg x1 x2) (avg y1 y2))))

(define (avg a b)
  (/ (+ a b) 2))
#| END |#