Aptitude - Odd Man Out and Series - Discussion

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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