# Aptitude - Odd Man Out and Series - Discussion

Discussion Forum : Odd Man Out and Series - Find Wrong No. (Q.No. 7)

*Directions to Solve*

Find out the wrong number in the series.

7.

1, 3, 10, 21, 64, 129, 356, 777

Answer: Option

Explanation:

A x 2 + 1, B x 3 + 1, C x 2 + 1, D x 3 + 1 and so on.

So, 356 is wrong.

Discussion:

10 comments Page 1 of 1.
Dhara said:
5 years ago

I think 64 should be the answer.

We are adding prime no 1 3 7 11 13 so 64 is wrong.

We are adding prime no 1 3 7 11 13 so 64 is wrong.

Aditya Kavlekar said:
5 years ago

As per my logic;.

Only 10 is multiple of 5 and rest are not. So odd one is 10.

Only 10 is multiple of 5 and rest are not. So odd one is 10.

Pradyumna said:
6 years ago

Thanks for the answers.

Anu said:
6 years ago

Thanks for the explanation.

Ankush said:
7 years ago

Agree @Imran.

Kuldeep choudhary said:
7 years ago

One more alternative method:-.

Separate out even & odd place numbers as 3, 21, 129, 777 & 1, 10, 64, 356.

Then find the difference between each other like 18, 108, 548 & 9, 54, 292.

Hereafter you will find the division of numbers are constant (i.e. Dividend=6), only 292 differs, then back this & 356 is the answer.

Separate out even & odd place numbers as 3, 21, 129, 777 & 1, 10, 64, 356.

Then find the difference between each other like 18, 108, 548 & 9, 54, 292.

Hereafter you will find the division of numbers are constant (i.e. Dividend=6), only 292 differs, then back this & 356 is the answer.

Sarvani said:
7 years ago

64 is a perfect square number, rest all are not.

Sweety said:
10 years ago

1, 3, 10, 21, 64, 129, 356, 777

3-1=2.

10-3=7.

21-10=11.

64-21=43.

129-64=65.

356-129=127.

777-356=421.

Answer should be 129. Because after subtracting in all the case give prime number except in 129-64 case.

3-1=2.

10-3=7.

21-10=11.

64-21=43.

129-64=65.

356-129=127.

777-356=421.

Answer should be 129. Because after subtracting in all the case give prime number except in 129-64 case.

(1)

Imran said:
1 decade ago

a-1 and b=3 take first two number as a and b

1*2+1=3

3*3+1=10

10*2+1=21

21*3+1=64

64*2+1=129

129*3+1=388 but in the queston in 356 so 356 is worng

388*2+1=777

Is it clear 356 is wrong

1*2+1=3

3*3+1=10

10*2+1=21

21*3+1=64

64*2+1=129

129*3+1=388 but in the queston in 356 so 356 is worng

388*2+1=777

Is it clear 356 is wrong

(3)

Nagendramurthy said:
1 decade ago

Alternate method:

1=1

3=3

10=1+0=1

21=2+1=3

64=6+4=10=1+0=1

129=1+2+9=12=1+2=3

356=3+5+6=14=1+4=5( wrong one.. it should be 1)

777=7+7+7=21=2+1=3

Alternative 1 and 3 series.. this is method is correct..

1=1

3=3

10=1+0=1

21=2+1=3

64=6+4=10=1+0=1

129=1+2+9=12=1+2=3

356=3+5+6=14=1+4=5( wrong one.. it should be 1)

777=7+7+7=21=2+1=3

Alternative 1 and 3 series.. this is method is correct..

(1)

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