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    Question

    Find the last digit of (12123 –

    1).
    A 5 Correct Answer Incorrect Answer
    B 8 Correct Answer Incorrect Answer
    C 7 Correct Answer Incorrect Answer
    D 6 Correct Answer Incorrect Answer

    Solution

    Cyclicity of 2: 21 = 2,  2 2 = 4,  2 3 = 8,  2 4 = 16,  2 5 = 32 Hence, we can see the last digits repeat themselves after every power of 4. So, Units digit of (12123 – 1) = Unit digit of {2(4 × 30 + 3) – 1} = {23 – 1} = 8 – 1 = 7

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