is x a prime number?

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is x a prime number?

by himu » Tue Jul 09, 2013 7:27 pm
If x and y are positive integers, is x a prime number?
(1) |x−2|<2−y.

(2) x+y−3=|1−y|.

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by [email protected] » Tue Jul 09, 2013 7:50 pm
Hi himu,

This DS question is perfect for the Empowergmat tactic TEST IT.

We're told that x and y are POSITIVE INTEGERS. The prompt asks "Is x prime?" This is a Yes/No question.

Fact 1 gives us |x - 2| < 2 - y

There's an interesting number property here because the left hand side can never be less than 0 and the right hand side can be no greater than 1

If y = 1, then x = 2 The answer is YES, but....
There's only one possible value for x. By definition, that is SUFFICIENT.

Fact 2 gives us x + y - 3 = |1 - y|
If y = 1, then x = 2 The answer is YES
If y = 2, then x = 1 The answer is NO
Inconsistent = INSUFFICIENT

Final Answer: A (1 only is SUFFICIENT

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
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by Matt@VeritasPrep » Fri Jul 12, 2013 1:33 pm
I may be missing something here, but the second statement looks sufficient.

Assuming x and y are positive integers, the second statement gives us

x + y - 3 = (y - 1)

since for all y greater than or equal to 1, |1 - y| = (y - 1).

Adding 3 to both sides, we have x + y = y + 2, or x = 2, so x is a prime number.

Rich, I think your numbers are off in your explanation - if y = 2, x = 2.