How Many Numbers Can Be Formed with the Digits 1, 2, 3, 4, 3, 2, 1 So that the Odd Digits Always Occupy the Odd Places? - Mathematics | Shaalaa.com

ZIP 4 Code lookup, get last 4 digits of 9-digit ZIP Code

The U.S. Postal Service uses two kinds of zip codes. One short form uses five digits, like 20906. The longer form uses nine digits, like 20742-3053. a. How many five-digit zip codes are possible? b. How many nine-digit zip codes are possible? c. How do your answers to Parts a and b explain the fact that every possible U.S. mail address has a unique nine-digit zip code but not a unique five-digit code? | Numerade