# Aptitude - Odd Man Out and Series - Discussion

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

*Directions to Solve*

Find out the wrong number in the series.

10.

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

Answer: Option

Explanation:

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

So, 39 is wrong.

Discussion:

8 comments Page 1 of 1.
Nani said:
6 years ago

All are divisible by 3. But 7 can't be divisible. So, why can't that be the answer?

(1)

R@m said:
7 years ago

The another logic is 2^2 - 1, 2^3 - 1, 2^4 - 1, .....

Poooja said:
7 years ago

Thank you for your clear answer.

Mehtab said:
8 years ago

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.

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.

Siva said:
8 years ago

Please clear explain.

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.

.

.

7+8 = 15.

15+16 = 31.

31+32 = 63.

63+64 = 127.

127+128 = 255.

255+256 = 511.

.

.

Shruti said:
1 decade ago

It can also be solved like such---

2^2-1,2^3-1,2^4-1,2^5-1 and so on....

2^2-1,2^3-1,2^4-1,2^5-1 and so on....

Ashik Mohammed Nazar said:
1 decade ago

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 ...

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 ...

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