;; The first three lines of this file were inserted by DrScheme. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname interest) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
;; Contract: number -> number

;; Purpose: determine a yearly interest rate based on amount
;; The interest rate is 0.04 for amounts between 0 and
;; 1000 (incl), 0.045 for amounts between 1000 and 5000 (incl),
;; and 0.05 for larger amounts. 

;; Examples: (interest-rate 500) -> 0.04
;; (interest-rate 1000) -> 0.04
;; (interest-rate 10000) -> 0.05
(define (interest-rate amount)
  (cond
  [(< amount 0) 0.0]
  [(<= amount 1000) .04]
  [(<= amount 5000) .045]
  [(> amount 5000) 0.05]  
  ) 
)

;; Tests
(interest-rate 500) 
;; expected value
0.04

(interest-rate 1000) 
;; expected value
0.04

(interest-rate 10000) 
;; expected value
0.05

(interest-rate -500) 
;; expected value
0.0

(interest-rate 3000) 
;; expected value
0.045

;; Write a function that, given an amount of money,
;; computes the interest on that amount that accumulates in a year