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In "Number Series" question, a number series is given with one term missing. Choose the correct alternative that will same pattern and fill in the blank spaces

In following question, a number series is given with one term missing. Choose correct alternative

15,31,63,127,255,x

Option:
A. 513
B. 511
C. 517
D. 523
Answer: B . 511

Justification:

(1) Each number is double the preciding one plus

      1 ( 255 * 2 ) + 1 = 511

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