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

Find out the incorrect number 1, 5, 5, 9, 7, 11, 11, 15, 12, 17

Option:
A. 11
B. 12
C. 17
D. 15
Answer: B . 12

Justification:

The given sequence is a combination of two series :
I.    1, 5, 7, 11, 12   and
II.   5, 9, 11, 15, 17
The pattern in both I and II is + 4, + 2, + 4, + 2.
So, 12 is wrong and must be replaced by (11 + 2)  i.e. 13.

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