How many 9 digit zip codes are possible if the first digit cannot be 0?
If repeats are allowed: 9 x 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 =9 x 10^8 =900,000,000
if repeats are not allowed: 9 x 10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 =9 x 10! / 2 =16,329,600
+142 
