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Prime Number

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Prime Number [#permalink] New post 15 Jul 2013, 22:41
If x is an integer, what is the value of x?

(1) |23x| is a prime number.

(2) 2x^{\frac{1}{2}} is a prime number.

GMAT Club test set the correct answer as (E), as they conclude x could be 1 or -1. But Is prime number can be negative? So my answer would be (D) as x=1
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Re: Prime Number [#permalink] New post 16 Jul 2013, 20:33
Expert's post
guhabiswasavijit wrote:
If x is an integer, what is the value of x?

(1) |23x| is a prime number.

(2) 2x^{\frac{1}{2}} is a prime number.

GMAT Club test set the correct answer as (E), as they conclude x could be 1 or -1. But Is prime number can be negative? So my answer would be (D) as x=1


Prime numbers are always positive.

(1) |23x| is a prime number.
Here, x can be 1 or -1

x = 1: |23x| = 23 (a prime number)
x = -1: |23x| = |23(-1)| = |-23| = 23 (a prime number) (the mod converts the negative to positive)

(2) 2x^{\frac{1}{2}} is a prime number.
Are you sure the actual question doesn't say 2x^{2} is a prime number?
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Re: Prime Number [#permalink] New post 16 Jul 2013, 20:46
guhabiswasavijit wrote:
If x is an integer, what is the value of x?

(1) |23x| is a prime number.

(2) 2x^{\frac{1}{2}} is a prime number.

GMAT Club test set the correct answer as (E), as they conclude x could be 1 or -1. But Is prime number can be negative? So my answer would be (D) as x=1

Actually with the given options, answer must be B, as it would yield x=1.

However for the answer to be E, the statement 2 must have x^2 instead of x^1/2 as karishma pointed out.
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Re: Prime Number [#permalink] New post 16 Jul 2013, 21:34
Vips0000 wrote:
guhabiswasavijit wrote:
If x is an integer, what is the value of x?

(1) |23x| is a prime number.

(2) 2x^{\frac{1}{2}} is a prime number.

GMAT Club test set the correct answer as (E), as they conclude x could be 1 or -1. But Is prime number can be negative? So my answer would be (D) as x=1

Actually with the given options, answer must be B, as it would yield x=1.

However for the answer to be E, the statement 2 must have x^2 instead of x^1/2 as karishma pointed out.


Actually, I formatted the question and that is exactly what I was thinking when I was doing that.... Or maybe I got confused by the layout.. :oops:
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Re: Prime Number [#permalink] New post 17 Jul 2013, 09:54
MacFauz wrote:
Vips0000 wrote:
guhabiswasavijit wrote:
If x is an integer, what is the value of x?

(1) |23x| is a prime number.

(2) 2x^{\frac{1}{2}} is a prime number.

GMAT Club test set the correct answer as (E), as they conclude x could be 1 or -1. But Is prime number can be negative? So my answer would be (D) as x=1

Actually with the given options, answer must be B, as it would yield x=1.

However for the answer to be E, the statement 2 must have x^2 instead of x^1/2 as karishma pointed out.


Actually, I formatted the question and that is exactly what I was thinking when I was doing that.... Or maybe I got confused by the layout.. :oops:

Lol.. :twisted:
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Re: Prime Number [#permalink] New post 17 Jul 2013, 22:17
Yes, the question says 2*\sqrt{x} is a prime number. Got it, Thanks.
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Re: Prime Number [#permalink] New post 21 Jul 2013, 10:23
Expert's post
guhabiswasavijit wrote:
If x is an integer, what is the value of x?

(1) |23x| is a prime number.

(2) 2x^{\frac{1}{2}} is a prime number.

GMAT Club test set the correct answer as (E), as they conclude x could be 1 or -1. But Is prime number can be negative? So my answer would be (D) as x=1



The question reads:
If x is an integer, what is the value of x?

(1) |23x| is a prime number.
(2) 2\sqrt{x^2} is a prime number.

The correct answer is E.

If x is an integer, what is the value of x?

(1) |23x| is a prime number. From this statement it follows that x=1 or x=-1. Not sufficient.

(2) 2\sqrt{x^2} is a prime number. The same here: x=1 or x=-1. Not sufficient.

(1)+(2) x could be 1 or -1. Not sufficient.

Answer: E.
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Re: Prime Number   [#permalink] 21 Jul 2013, 10:23
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