#lang sicp

(define (make-interval a b) (cons a b))

(define (lower-bound i)
	(car i))

(define (upper-bound i)
	(cdr i))


(define (make-center-percent c p)
  (make-interval (- c (* c p 1/100))
                 (+ c (* c p 1/100))))

(define (center i)
  (/ (+ (lower-bound i) (upper-bound i)) 2))

(define (width i)
  (/ (- (upper-bound i) (lower-bound i)) 2))

(define (percent i)
  (* (/ (width i) (center i)) 100))