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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 number series, two terms have been put within brackets. Choose the appropriate option

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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