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    Question

    Find the unit digit of (57 129  -

    7).
    B 2 Correct Answer Incorrect Answer
    C 6 Correct Answer Incorrect Answer
    D 4 Correct Answer Incorrect Answer

    Solution

    Cyclicity of 7 = 7, 9, 3, 1, 7

    Hence, we can see the last digits repeat themselves after every power of '4'.

    So, unit digit of 57 129  = units digit of 7 (128 + 1)  = 7 {Since, (128/4) = 32}

    So, unit digit of 57 129  - 7 = unit digit of 7 1  - 7 = 7 - 7 = 0

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