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 500,000 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:

0% (00:00) correct
0% (00:00) wrong based on 0 sessions

HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Hi all,

I need some help please. This is the question :

If x^2 = y + 5, y = z - 2 , and z = 2x, is X^3 + y^2 + z divisible by 7?

1. x > 0

2. y = 4

Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient EACH statement ALONE is sufficient Statements (1) and (2) TOGETHER are NOT sufficient

Re: DS from GMAT Club Test - Need Help ! [#permalink]

Show Tags

22 Dec 2009, 17:01

I think the answer is (B).

You have x^2 = y + 5, y = z - 2, & z = 2x.

Combine y = z - 2 & z = 2x. You get y = 2x - 2. Put this new equation in x^2 = y + 5. You get x^2 = 2x - 2 + 5. Put it in quadratic form and you get x^2 - 2x -3 = 0, which is (x-3)(x+1). x = 3, or x = -1. This means that these are the only x-values that will satisfy these 3 equations simultaneously. If you use x= 3 to get the other values, you'll get z = 6 & y = 4. If you plug in these values into that equation to see if it is divisible by 7, you'll see that the result is 49 and so it is divisible. This is the only value that will both satisfy the equations and be divisible by 7. Any other x-value will either not satisfy the 3 equations and/or be divisible by 7. x = -1 does not matter since you're only looking at x > 0. So (A) does not give enough information.

For (B), y = 4. Looking at my work above, you'll see that if y = 4, then z = 6, & x = 3, which satisfies the equations and will give you a result that is divisible by 7. So I think (B) is the answer.

Re: DS from GMAT Club Test - Need Help ! [#permalink]

Show Tags

23 Dec 2009, 02:20

Thank you ! Very Nice.

But can you please detail how you get the x^2-2x-3 = 0 equation. I understand that you put x in z and y, but I do not manage to reach this last equation. Otherwise, your explanations look clear.

Re: DS from GMAT Club Test - Need Help ! [#permalink]

Show Tags

23 Dec 2009, 03:05

nesta wrote:

Thank you ! Very Nice.

But can you please detail how you get the x^2-2x-3 = 0 equation. I understand that you put x in z and y, but I do not manage to reach this last equation. Otherwise, your explanations look clear.

Re: DS from GMAT Club Test - Need Help ! [#permalink]

Show Tags

23 Dec 2009, 03:53

I sorry but I missed something. I cannot reach the final equation. It looks easy but...

So, I agree with you :

1.x^2=2x+3 --> We need x^3, no ? How do you get it ? 2.y = 2x - 2 3.z = 2x We are looking for x^3 + y^2 + z, right ? So do you substitute these 3 equations into x^3+ y^2 + z to get x^3+(2x-2)^2+2x ?

Re: DS from GMAT Club Test - Need Help ! [#permalink]

Show Tags

23 Dec 2009, 04:05

1

This post received KUDOS

nesta wrote:

Quote:

Quote:

I sorry but I missed something. I cannot reach the final equation. It looks easy but...

So, I agree with you :

1.x^2=2x+3 --> We need x^3, no ? How do you get it ? 2.y = 2x - 2 3.z = 2x We are looking for x^3 + y^2 + z, right ? So do you substitute these 3 equations into x^3+ y^2 + z to get x^3+(2x-2)^2+2x ?

Thank you xcusemeplz2009 !

not necessary it will complicate the things to prove x^3+y^2+z is div by seven we need to knw the value of x,y,and z the eqn x^2-2x-3=0 gives x=3 or -1 with x=3 we get a value for y and z using the given relations and we come to know that its div. by 7 and with x=-1 we come to knw that its not div by 7 now the task is to know wether x is 3 or -1

s1) tells x>0 , and x=3 is the only +ve root of x^2-2x-3 hence suff s2) tells x=3 same as abve hence suff...

here now we want to ensure that is it div or not and if the statements wud have shown that x=-1 even then its suff...
_________________

GMAT is not a game for losers , and the moment u decide to appear for it u are no more a loser........ITS A BRAIN GAME

Re: DS from GMAT Club Test - Need Help ! [#permalink]

Show Tags

23 Dec 2009, 04:27

Really Thx xcusemeplz2009 !

I get it ! I tried to find x^3 + y^2 + z with substitution, that is why I do not reach your last equation. You right, we got x^2 = 2x+3 so x^2-2x-3 = 0, then factorization ect...