# Aptitude - Odd Man Out and Series - Discussion

### Discussion :: Odd Man Out and Series - Find Wrong No. (Q.No.10)

Find out the wrong number in the series.

10.

3, 7, 15, 39, 63, 127, 255, 511

 [A]. 7 [B]. 15 [C]. 39 [D]. 63 [E]. 127

Explanation:

Go on multiplying 2 and adding 1 to get the next number.

So, 39 is wrong.

 Ashik Mohammed Nazar said: (Jun 7, 2011) 3,7,15,39,63,127,255,511 If u closely look at this pattern,and the differences between the consecutive numbers, It is 4 8 24 24 64 128 256 By changing 39 to 31, the differences become 4 8 16 32 64 128 256 which is 2^2 2^3 2^3 2^4 and so on ...

 Shruti said: (Aug 22, 2012) It can also be solved like such--- 2^2-1,2^3-1,2^4-1,2^5-1 and so on....

 Grace said: (Jan 28, 2014) 3+4 = 7. 7+8 = 15. 15+16 = 31. 31+32 = 63. 63+64 = 127. 127+128 = 255. 255+256 = 511. . .

 Siva said: (Dec 20, 2015) Please clear explain.

 Mehtab said: (Apr 7, 2016) 3*2 + 1 = 7 7*2 + 1 = 15 15*2 + 1 = 31 31*2 + 1 = 63 63*2 + 1 = 127 127*2 + 1 = 255 255*2 + 1 = 511 31 is given instead of 31. 39 is the wrong answer.

 Poooja said: (Jun 30, 2016) Thank you for your clear answer.

 R@M said: (Jul 18, 2016) The another logic is 2^2 - 1, 2^3 - 1, 2^4 - 1, .....

 Nani said: (May 1, 2018) All are divisible by 3. But 7 can't be divisible. So, why can't that be the answer?

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