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GPREP problem

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GPREP problem

by aj5105 » Sun Jan 11, 2009 8:15 am
If x is an integer, is (x^2 + 1)(x + 5) an even number?

1)X is an odd number
2)Each prime factor of x^2 is greater than 7.
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Re: GPREP problem

by duccio » Sun Jan 11, 2009 11:07 am
aj5105 wrote:If x is an integer, is (x^2 + 1)(x + 5) an even number?

1)X is an odd number
2)Each prime factor of x^2 is greater than 7.

Hi,
which is the OA? D?
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Re: GPREP problem

by Stuart@KaplanGMAT » Sun Jan 11, 2009 11:08 am
aj5105 wrote:If x is an integer, is (x^2 + 1)(x + 5) an even number?

1)X is an odd number
2)Each prime factor of x^2 is greater than 7.
To get an even product, we need at least one of the terms to be even.

(x^2 + 1) will be even whenever x is odd. (x + 5) will be even whenever x is odd.

So, the question really is: Is x odd?

(1) sufficient!

(2) whenever you see primes in DS, think about "2", the only even prime number.

If all the prime factors of x^2 are greater than 7, then 2 is NOT a prime factor of x. Therefore, x is odd: sufficient.

Each of (1) and (2) are sufficient alone: choose (D).
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