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In following questions, one term in number series is incorrect.

Find out the incorrect number 1, 3, 7, 15, 27, 63, 127

Option:
A. 7
B. 15
C. 27
D. 63
Answer: C . 27

Justification:

The sequence is + 2, + 4, + 8,....  i.e. + 2, + 22, + 23,....
So, 27 is wrong and must be replaced by (15 + 24) i.e. (15 +16) or 31.

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