Aptitude - Odd Man Out and Series - Discussion

{2*2=4, 4*1=4, 1*4=4}.....>.....4.

{3*2=6, 2*3=6, 6*1=6, 1*6=6}.....>.....6.

{4*2=8, 2*4=8, 8*1=8, 1*8=8}.....>.....8.

{3*3=9, 9*1=9, 1*9=9}.....>.....9.

{2*5=10, 5*2=10, 1*10=10, 10*1=10}.....>.....10.

{6*2=12, 2*6=12, 12*1=12, 1*12=12}.....>.....12.

All this no, have factors including factor of itself. Factor of it self i.e. [Example: 1*2, 2*1 ]. But only 11 in the option which has factors for itself we can't get 11 by multiplying with other no. s.

Its factor is {1*11, 11*1}.....>.....11.

This is the factors of 11. Now I hope Lavkush you may got atleast some idea why only 11 why not 9.

This is a flawed question. They should update it.

They use the word 'composite' to mean non-prime. Every number is either prime (divisible only by itself and one) or non-prime (having factors other than itself and one).

The question uses a sequence of natural numbers: 7 4 6 8 9 10 11 12.

They describe every number except 11 as 'composite' (having other factors apart from itself and one) but 7 is also in that category. So they made a mistake. End of story.

COMPOSITE NUMBERS MEANS : NUMBERS WHICH ARE DIVIDED BY ITSELF AND ONE AND ALSO OTHER THAN ONE OR ITSELF. For e.g 9 is divided by one, it gets divided by itself (i.e 9) and also other numbers is 3. So 9 is comp.

Whereas 11 is divided by one and 11 itself but there is no other numbers except one and itself, so its not comp. OK, guys I hope you understand this :).

If any number has more then two factors(1 and that number itself) then that number is called composite number.

Example:

9 has 1,3,9 as factor ,so its composite number.

11 has 1,11 as the factor so it is not composite number since it is divisible by 1 and by that number itself.

11 is a prime number so it became odd member of the series.
Any number which is divisible by 1 and itself is a prime number, and any number which is not prime is called a composite number.
But one does not belong to both these categories i.e., prime or composite.

Here 11 is only the prime number in the numbers given above.

All other numbers 4, 6, 8, 10, 12 are divisible by 2, and number nine is divisible by 3 so these are not the prime numbers.

Hence, "11" is the odd one here.

Yes.
A composite number is a positive integer which has a positive divisor other than one or itself. In other words a composite number is any positive integer greater than one that is not a prime number.

Composite no. Means it is divisible by its factor &itsself also or having more than 2 factors.

Its very clear 4, 6, 8, 10, 12, 9 has more than 2 factor but 11 has only 1&11.

Here the logic is;

Consider 4,8,10 and 12. They are divisible by 2. Now consider 6,9 and 11. 6 and 9 are divisible by 3 but 11 can't be divided by 3.

So the answer is 11.

9 has 3 factors : 9, 3, 1 so it is composite number.

But 11 has not any other factor except 11 and 1.

So it is not a composite number, it is a prime number.