# Aptitude - Odd Man Out and Series - Discussion

### Discussion :: Odd Man Out and Series - Missing No. (Q.No.12)

Insert the missing number.

12.

15, 31, 63, 127, 255, (....)

 [A]. 513 [B]. 511 [C]. 517 [D]. 523

Answer: Option B

Explanation:

Each number is double the preceding one plus 1.

So, the next number is (255 x 2) + 1 = 511.

 Ardyula Dattatreya Sarma said: (Aug 25, 2012) Another way to answer it the difference between number is increased double 15+16=31 31+32=63 63+64=127 127+128=255 255+256=511

 Gowtham Mx said: (Jun 9, 2013) My view of the problem: (2*2*2*2)-1 = 15. (2 to the power 5)-1 = 31. And so on, finally, (2 to the power 9)-1 = 512-1 = 511.

 Yogesh said: (Oct 12, 2014) Previous number "255" ending with 5. Comparing similar characteristics with the numbers in series. We can observe that "15" ending with 5 and has the next number "31" By this we can predict that the next number of "255" must end with "1" ANSWER: 511.

 Mukesh said: (Sep 11, 2016) 15 x 2 = 30 + 1 = 31, 31 x 2 = 62 + 1 = 63, 63 x 2 = 126 + 1 = 127, So, 255 x 2 = 510 + 1 = 511.

 Eamon said: (Dec 28, 2016) #1 = 1 #2 = 1 + 1 + 1 = 3 #3 = 3 + 3 + 1 = 7 #4 = 7 + 7 + 1 = 15 #5 = 15 + 15 + 1 = 31 #6 = 31 + 31 + 1 = 63 #7 = 63 + 63 + 1 = 127 #8 = 127 + 127 + 1 = 255 #9 = 255 + 255 + 1 = 511.

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