What is the <strong>LARGEST</strong> number which divides both 2^{35}-1 and 2^{91}-1?

  1. A. 34
  2. B. 90
  3. C. 127
  4. D. 129

Correct Answer: C. 127

Explanation

Using the property \text{HCF}(a^m-1, a^n-1) = a^{\text{HCF}(m,n)} - 1. Since \text{HCF}(35, 91) = 7, the largest dividing number is 2^7 - 1 = 127.

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