# Chapter 11 - 11.6 - Counting Principles - 11.6 Exercises - Page 823: 24b

$4536$ four-digit numbers are possible.

#### Work Step by Step

First digit: 9 choices Second digit: 9 choices Third digit: 8 choices Fourth digit: 7 choices Using the Fundamental Counting Principle: $9\times9\times8\times7=4536$

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