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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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