crackitpal wrote:If x and y are integers, is the value x(y+1) even ?

1. x and y are prime numbers
2. y > 7

I went with A. Because I thought x and y could be any prime numbers from 2 to n. Apart from number 2 all prime numbers are odd. So x(y+1) will have atleast one even number making it even. Am I wrong ? The solution from GMATPrep is C.

Please let me know, I'm going to give exam on Saturday . Don't feel quite prepared.

Thanks.

Stuart Kovinsky wrote:

crackitpal wrote:If x and y are integers, is the value x(y+1) even ?

1. x and y are prime numbers
2. y > 7

I went with A. Because I thought x and y could be any prime numbers from 2 to n. Apart from number 2 all prime numbers are odd. So x(y+1) will have atleast one even number making it even. Am I wrong ? The solution from GMATPrep is C.

Please let me know, I'm going to give exam on Saturday . Don't feel quite prepared.

Thanks.

If you pick x = 3 and y = 2, then x(y+1) = 3(3) = 9 which is odd. Only by adding in y>7 do we know that y must be an odd integer, which means that x(y+1) = x(even) = even.

750Goal wrote:Hi Stuart.

In regard to solution provided to this problem long time ago, I may be asking a silly question, but would like
to clarify your solution.

Below you say y>7 = even, but y could be 8,9,10.... and by adding 1 , it would make it even or odd,
therefore it is not only even but also odd... I think I may be missing something here,
could you please clarify at earliest.

Thanks in advance.
Parag

capthan wrote:Hi Stuart,
x can be 2 or 3 and in both case x is prime, and if y>7 it will give you two different answers. IMO the answer is e.