# Aptitude - Odd Man Out and Series - Discussion

Discussion Forum : Odd Man Out and Series - Find Wrong No. (Q.No. 15)

*Directions to Solve*

Find out the wrong number in the series.

15.

3, 7, 15, 27, 63, 127, 255

Answer: Option

Explanation:

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

So, 27 is wrong.

Discussion:

12 comments Page 1 of 2.
Sivaji Pulluru said:
4 years ago

3*2 = 6 + 1 = 7

7*2 = 14 + 1 = 15

15*2 = 30 + 1 = 31

31*2 = 62 + 1 = 63.

7*2 = 14 + 1 = 15

15*2 = 30 + 1 = 31

31*2 = 62 + 1 = 63.

Minu said:
5 years ago

3+4 = 7

7+8 = 15

15+12 = 27

27+16 = 43

7+8 = 15

15+12 = 27

27+16 = 43

Rehan said:
6 years ago

Every alternate number is divisible by 3, so 27 is not according to sequence.

Rohan said:
7 years ago

Yes, right @Major Sandhu.

Manikandan said:
8 years ago

2^2 - 1 = 3,

2^3 - 1 = 7,

2^4 - 1 = 15,

2^5 - 1 = 31(not 27),

2^6 - 1 = 63.

And so on...

2^3 - 1 = 7,

2^4 - 1 = 15,

2^5 - 1 = 31(not 27),

2^6 - 1 = 63.

And so on...

Sunder said:
8 years ago

All the numbers can be divided by 3 except and 127 and 7.

Major sandhu said:
1 decade ago

4-1 = 3.

8-1 = 7.

16-1 = 15.

32-1 = 31.

8-1 = 7.

16-1 = 15.

32-1 = 31.

Grace said:
1 decade ago

3+4 = 7.

7+8 = 15.

15+16 = 31.

*31+32 = 63.

63+64 = 127.

127+128 = 255.

255+256 = 511.

Here the series we are adding is 4,8,16,32,64,128,256....so on.

Hence 27 is the only wrong answer.

7+8 = 15.

15+16 = 31.

*31+32 = 63.

63+64 = 127.

127+128 = 255.

255+256 = 511.

Here the series we are adding is 4,8,16,32,64,128,256....so on.

Hence 27 is the only wrong answer.

Xyz said:
1 decade ago

Why can't it be like this:

3*1+4 = 7

7*1+8 = 15

15*1+12 = 27

27*1+16 = 43

So 63 can also be the wrong answer.

3*1+4 = 7

7*1+8 = 15

15*1+12 = 27

27*1+16 = 43

So 63 can also be the wrong answer.

Shakshi said:
1 decade ago

According to this logic:

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

3*2+1=7

7*2+1=15

15*2+1=31

31*2+1=63

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

3*2+1=7

7*2+1=15

15*2+1=31

31*2+1=63

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