Problem 3. How many 7-digit numbers have no two adjacent digits equal.
Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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Transcribed Image Text:Problem 3. How many 7-digit numbers have no two adjacent digits equal.
Expert Solution
Step 1
To count the number of 7-digit numbers with no two adjacent digits equal, we can use the following approach:
First, choose the first digit of the 7-digit number, which can be any of the 9 digits from 1 to 9 (since 0 cannot be the first digit of a 7-digit number).
Next, for the second digit, we can choose any of the 9 remaining digits (since we cannot choose the same digit as the first one), which gives us 9 choices.
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