Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 350,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

My choice was B although I knew it was probably E (which it turned out it was). Here's my problem with statement 2: if we know what that 2√x²=prime number, then why can't we conclude that x=1? Let's assume that x= -1, then according to the equation we would have 2√x²=positive value. but knowing that x= -1 we know that the equation would become 2*(-1)= -2 # 2 (since we know we would have to use the negative root since x= -1). but from statement 2 we know that it must be positive so x can only be positive 1. I know that technically the definition for √x² is |x| but in this case it does not make sense for me. for statement 1 it's no problem, since |x| dictates to multiply by (-1) if negative, but in the case of statement 2, x should only be positive, since otherwise we would have to take the negative square root and then the result would not be positive anymore. I hope I made it clear why I am confused. Maybe someone could help me

cheers,

Max

Last edited by damamikus on 26 Feb 2014, 02:23, edited 1 time in total.

Re: M04#07 If x is an integer, what is the value of x? [#permalink]
26 Feb 2014, 01:50

Expert's post

damamikus wrote:

If x is an integer, what is the value of x? (1) |23x| is a prime number.

(2) 2√x² is a prime number.

My choice was B although I knew it was probably E (which it turned out it was). Here's my problem with statement 2: if we know what that 2√x²=prime number, then why can't we conclude that x=1? Let's assume that x= -1, then according to the equation we would have 2√x²=positive value. but knowing that x= -1 we know that the equation would become 2*(-1)= -2 # 2 (since we know we would have to use the negative root since x= -1). but from statement 2 we know that it must be positive so x can only be positive 1. I know that technically the definition for √x² is |x| but in this case it does not make sense for me. for statement 1 it's no problem, since |x| dictates to multiply by (-1) if negative, but in the case of statement 2, x should only be positive, since otherwise we would have to take the negative square root and then the result would not be positive anymore. I hope I made it clear why I am confused. Maybe someone could help me

cheers,

Max

If x=-1, then 2\sqrt{x^2}=2\sqrt{(-1)^2}=2\sqrt{1}=2.

Complete solution:

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.

Re: M04#07 If x is an integer, what is the value of x? [#permalink]
26 Feb 2014, 02:07

I think i get it now: since 2√x² must be positive, i am taking the positive square root out of the square-root expression x². but the value that lead to the positive expression inside the square root could be negative or positive. --> x²=z --> 2√z=positive, hence z=positive. but what lead to z being positive (--> x ) could be either negative or positive, since in both cases z would be positive. hope this reasoning is correct

Re: M04#07 If x is an integer, what is the value of x? [#permalink]
03 Mar 2014, 04:49

Bunuel wrote:

damamikus wrote:

If x is an integer, what is the value of x? (1) |23x| is a prime number.

(2) 2√x² is a prime number.

My choice was B although I knew it was probably E (which it turned out it was). Here's my problem with statement 2: if we know what that 2√x²=prime number, then why can't we conclude that x=1? Let's assume that x= -1, then according to the equation we would have 2√x²=positive value. but knowing that x= -1 we know that the equation would become 2*(-1)= -2 # 2 (since we know we would have to use the negative root since x= -1). but from statement 2 we know that it must be positive so x can only be positive 1. I know that technically the definition for √x² is |x| but in this case it does not make sense for me. for statement 1 it's no problem, since |x| dictates to multiply by (-1) if negative, but in the case of statement 2, x should only be positive, since otherwise we would have to take the negative square root and then the result would not be positive anymore. I hope I made it clear why I am confused. Maybe someone could help me

cheers,

Max

If x=-1, then 2\sqrt{x^2}=2\sqrt{(-1)^2}=2\sqrt{1}=2.

Complete solution:

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.

Hope it's clear.

Dear Bunuel

If x = -1 or x=1 then it will give -23 or 23. Can negative numbers be prime numbers?

Re: M04#07 If x is an integer, what is the value of x? [#permalink]
03 Mar 2014, 04:52

Expert's post

sidpopy wrote:

Bunuel wrote:

damamikus wrote:

If x is an integer, what is the value of x? (1) |23x| is a prime number.

(2) 2√x² is a prime number.

My choice was B although I knew it was probably E (which it turned out it was). Here's my problem with statement 2: if we know what that 2√x²=prime number, then why can't we conclude that x=1? Let's assume that x= -1, then according to the equation we would have 2√x²=positive value. but knowing that x= -1 we know that the equation would become 2*(-1)= -2 # 2 (since we know we would have to use the negative root since x= -1). but from statement 2 we know that it must be positive so x can only be positive 1. I know that technically the definition for √x² is |x| but in this case it does not make sense for me. for statement 1 it's no problem, since |x| dictates to multiply by (-1) if negative, but in the case of statement 2, x should only be positive, since otherwise we would have to take the negative square root and then the result would not be positive anymore. I hope I made it clear why I am confused. Maybe someone could help me

cheers,

Max

If x=-1, then 2\sqrt{x^2}=2\sqrt{(-1)^2}=2\sqrt{1}=2.

Complete solution:

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.

Hope it's clear.

Dear Bunuel

If x = -1 or x=1 then it will give -23 or 23. Can negative numbers be prime numbers?

Thanks

No, only positive integers can be primes (the smallest prime is 2).

Now, if x=-1, then |23x|=|23*(-1)|=|-23|=23. I think you missed modulus sign there |23x|.