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How many 9 digit zip codes are possible if the first digit cannot be 0?

 Apr 28, 2019
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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

 Apr 28, 2019

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