# 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
7
15
27
63
127
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:   3 years ago
3*2 = 6 + 1 = 7
7*2 = 14 + 1 = 15
15*2 = 30 + 1 = 31
31*2 = 62 + 1 = 63.

Minu said:   4 years ago
3+4 = 7
7+8 = 15
15+12 = 27
27+16 = 43

Rehan said:   5 years ago
Every alternate number is divisible by 3, so 27 is not according to sequence.

Rohan said:   6 years ago
Yes, right @Major Sandhu.

Manikandan said:   7 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...

Sunder said:   7 years ago
All the numbers can be divided by 3 except and 127 and 7.

Major sandhu said:   9 years ago
4-1 = 3.
8-1 = 7.
16-1 = 15.
32-1 = 31.

Grace said:   10 years 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.

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.

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

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