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Re: Is 12 is in K? [#permalink]
24 May 2011, 08:17

Baten80 wrote:

K is a set of numbers such that...

i) if x is in K, then -x is in K, and ii) if each of x and y is in K, then xy is in K.

Is 12 in K?

1) 2 is in K. 2) 3 is in K.

Solution: (1) 2 is in k so k includes 2,-2, -4, 8, 16, -32 but not 12 (2) 3 is in k so k includes 3, -3, -9, 27 but not 12 For C -3*-4= 12 [Ans. C]

I have different reasoning problem with this question The question is asking whether 12 is in k? so answer could be yes or no

Using the both options separately we can see 12 is not is in K, and using the both options together we can see 12 is K.

So to me answer Answer is D, but you know the right answer is C.

Thus help is badly needed!

A. 2 is in K ... therefore -2 will be there ....according to first condition Also -4 and 4 will be there ..... According to 1st and 2nd condition 2*-2 = -4 But, wont get 12 as an ans

Also, it is not mentioned that how many numbers are present in K therefore, we can assume that other than 2 there can be more number e.g. 12 ...then we can or can not get the ans ... Thus , Option A is insufficient

B. this option is insufficient for the same above mentioned reason

But, combining 2 options tells us that K definitely contain3 and 2 ..thus 4 ...........as shown above and According to 2nd condition 3*4 = 12

Re: Is 12 is in K? [#permalink]
25 May 2011, 10:11

vyassaptarashi wrote:

Baten80 wrote:

K is a set of numbers such that...

i) if x is in K, then -x is in K, and ii) if each of x and y is in K, then xy is in K.

Is 12 in K?

1) 2 is in K. 2) 3 is in K.

Solution: (1) 2 is in k so k includes 2,-2, -4, 8, 16, -32 but not 12 (2) 3 is in k so k includes 3, -3, -9, 27 but not 12 For C -3*-4= 12 [Ans. C]

I have different reasoning problem with this question The question is asking whether 12 is in k? so answer could be yes or no

Using the both options separately we can see 12 is not is in K, and using the both options together we can see 12 is K.

So to me answer Answer is D, but you know the right answer is C.

Thus help is badly needed!

A. 2 is in K ... therefore -2 will be there ....according to first condition Also -4 and 4 will be there ..... According to 1st and 2nd condition 2*-2 = -4 But, wont get 12 as an ans

Also, it is not mentioned that how many numbers are present in K therefore, we can assume that other than 2 there can be more number e.g. 12 ...then we can or can not get the ans ... Thus , Option A is insufficient

B. this option is insufficient for the same above mentioned reason

But, combining 2 options tells us that K definitely contain3 and 2 ..thus 4 ...........as shown above and According to 2nd condition 3*4 = 12

Re: Is 12 is in K? [#permalink]
25 May 2011, 10:30

Baten80 wrote:

How the 12 will be in k?

Do read my post carefully .... i have explained in Option A ...since 2 is present 4 must be present

And according to option B ...3 is present

At the end of the post i have said that since 3 and 4 both are present then according to the 2nd condition i.e. ii) if each of x and y is in K, then xy is in K 3 = X and 4 = y and XY = 3*4 = 12 _________________