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    Question

    How many integers between 100 and 999 have all digits

    distinct?
    A 582 Correct Answer Incorrect Answer
    B 770 Correct Answer Incorrect Answer
    C 648 Correct Answer Incorrect Answer
    D 620 Correct Answer Incorrect Answer

    Solution

    ATQ,

    Hundreds digit: 1–9 → 9 choices Tens digit: any except chosen hundreds → 9 choices Units digit: any except previous two → 8 choices Total = 9 × 9 × 8 = 648

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