Answer:
648
Explanation:
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Conditions: Not allowed to start with 0 // No repeating digits
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9 possible ways for first digit (excluding 0, therefore 1-9)
e.g. 123, 234, 567
9 possible ways for second digit (excluding 0 and digit before 1-9)
e.g. 123, 124, 125
8 possible ways for third digit (excluding 0 and condition for second digit 1-9)
e.g. 789 is legit, but 788 is not
Multiply 9*9*8 to get an answer of 648
