Let r denote number system radix. The only value(s) of r that satisfy the equation 
(A) decimal 10
(B) decimal 11
(C) decimal 10 and 11
(D) any value > 2


Answer: (D)

Explanation: As we can see 121 contains digit ‘2’ which can’t be represented directly in base ‘2’ (as digits should be less than base) so number system must have   “r>2”.

Ans (D) part.

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