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:

When \(x=2\), then \(10y^2=(2+2)(2-2)=0\) --> \(y=0\).

Now, plug \(x=2\) into the answer choices and look for the option which does not give \(y=0\). Only option D gives the value of \(y\) different from zero.

Each week we'll be posting several questions from The Official Guide for GMAT® Review, 13th Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution.

We'll be glad if you participate in development of this project: 1. Please provide your solutions to the questions; 2. Please vote for the best solutions by pressing Kudos button; 3. Please vote for the questions themselves by pressing Kudos button; 4. Please share your views on difficulty level of the questions, so that we have most precise evaluation.

Thank you!

Its D.. it should be.. 5y^2=X^2/2-2 _________________

Bole So Nehal.. Sat Siri Akal.. Waheguru ji help me to get 700+ score !

A) dividing by 3 on either side gives the same equation as given in question stem ==> 3* 10y^2=3(x^2-4) ==> 3* 10^y = 3(x + 2)(x - 2) ==> Q B) diving by 2 on both side ==> 2* 10y^2=2 * (x-2)(x+2) ==> Q C) taking 4 to right hand side and solving ==> 10y^2=x^2 - 4 ==> 10y^2 = (x+2)(x-2) ==> Q D) multiplying both side by 2 ==> 10y^2=2x^2-4 ==> left hand side can't be factored to (x-2)(x+2). Hence, this is NOT equivalent to equation given in Q stem. We can stop here and mark option D. E) multiply both sides by 10 ==> 10 y^2=10 *(x^2-4)/10 ==> 10 y^2=(x^2-4) ==> 10 y^2=(x+2)(x-2)

** basic formula which should be known prior to solving this question =====> (A^2 - B^2) = (A+B)(A-B)

Other method to solve this Q is by substituting the values. The best value to take for "x" is 2 as it will make right hand side of the equation ZERO. _________________

Re: Which of the following equations is NOT equivalent to 10y^2= [#permalink]

Show Tags

12 Sep 2012, 12:49

3

This post received KUDOS

Which of the following equations is NOT equivalent to 10y^2=(x+2)(x-2) ? (A) 30y^2=3x^2-12 (B) 20y^2=(2x-4)(x+2) (C) 10y^2+4=x^2 (D) 5y^2=x^2-2 (E) y^2=(x^2-4)/10

The original equation reduces to 10y^2 = x^2 -4 Option 1 - 3 times of equation Option 2 - 2 times of equation Option 3 - Same as original of equation Option 4 - Answer (Skip this option & jump to option 5, which in turn is right. Thus using POE this will be the answer. To cross check one can solve it) Option 5 - 1/10 times of equation Answer D

Hope it helps _________________

If you like my Question/Explanation or the contribution, Kindly appreciate by pressing KUDOS. Kudos always maximizes GMATCLUB worth-Game Theory

If you have any question regarding my post, kindly pm me or else I won't be able to reply

When \(x=2\), then \(10y^2=(2+2)(2-2)=0\) --> \(y=0\).

Now, plug \(x=2\) into the answer choices and look for the option which does not give \(y=0\). Only option D gives the value of \(y\) different from zero.

Answer: D.

Kudos points given to everyone with correct solution. Let me know if I missed someone. _________________

When \(x=2\), then \(10y^2=(2+2)(2-2)=0\) --> \(y=0\).

Now, plug \(x=2\) into the answer choices and look for the option which does not give \(y=0\). Only option D gives the value of \(y\) different from zero.

Answer: D.

Kudos points given to everyone with correct solution. Let me know if I missed someone.

Hi bunuel,

You haven't given me kudos for the right solution? _________________

If you like my Question/Explanation or the contribution, Kindly appreciate by pressing KUDOS. Kudos always maximizes GMATCLUB worth-Game Theory

If you have any question regarding my post, kindly pm me or else I won't be able to reply

When \(x=2\), then \(10y^2=(2+2)(2-2)=0\) --> \(y=0\).

Now, plug \(x=2\) into the answer choices and look for the option which does not give \(y=0\). Only option D gives the value of \(y\) different from zero.

When \(x=2\), then \(10y^2=(2+2)(2-2)=0\) --> \(y=0\).

Now, plug \(x=2\) into the answer choices and look for the option which does not give \(y=0\). Only option D gives the value of \(y\) different from zero.

Answer: D.

Bunuel could we also use -2??

Thanks, C

Yes we can. We can use the same exact logic. _________________

Re: Which of the following equations is NOT equivalent to 10y^2= [#permalink]

Show Tags

26 Oct 2014, 06:14

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________

When \(x=2\), then \(10y^2=(2+2)(2-2)=0\) --> \(y=0\).

Now, plug \(x=2\) into the answer choices and look for the option which does not give \(y=0\). Only option D gives the value of \(y\) different from zero.

Answer: D.

How do you actually solve using smart numbers? When I did it, all of my answers were y=0, x=2.

Let's pick x=2, when this is plugged into the equation we get y=0. So we're going to plug in 2 for all x's that we see, when y = 0 that is our answer.

a. 30y^2=3x^2-12 3(2)^2-12 = 0, therefore y=0 when x=2

b. 20y^2=(2x-4)(x+2) (2(2)-4)(2+2) = 0, therefore y=0 when x=2

When \(x=2\), then \(10y^2=(2+2)(2-2)=0\) --> \(y=0\).

Now, plug \(x=2\) into the answer choices and look for the option which does not give \(y=0\). Only option D gives the value of \(y\) different from zero.

Answer: D.

How do you actually solve using smart numbers? When I did it, all of my answers were y=0, x=2.

Let's pick x=2, when this is plugged into the equation we get y=0. So we're going to plug in 2 for all x's that we see, when y = 0 that is our answer.

a. 30y^2=3x^2-12 3(2)^2-12 = 0, therefore y=0 when x=2

b. 20y^2=(2x-4)(x+2) (2(2)-4)(2+2) = 0, therefore y=0 when x=2

What am I doing wrong?

I think you are missing out on what the question is asking. It is asking to find the expression that will NOT give you the same value as \(10y^2=(x+2)(x-2)\)

When you do use, x=2, you get the following values of 'y'

A) 0 B) 0 C) 0 D) 2/5 E) 0

From the original expression you see that when you get y=0 for x=2 for options A-C and E.

Thus, with your 'smart numbers', D is the only expression that DOES NOT give you the same values on the left hand side as those on the right hand side. D is thus the correct answer.

FYI, using smart numbers is not the best strategy for this question. You need to realize that \((A+B)(A-B) = A^2-B^2\) and thus the original expression becomes \(10y^2 = x^2-4\)

D will not give you this expression and is thus the correct answer. _________________

When \(x=2\), then \(10y^2=(2+2)(2-2)=0\) --> \(y=0\).

Now, plug \(x=2\) into the answer choices and look for the option which does not give \(y=0\). Only option D gives the value of \(y\) different from zero.

Answer: D.

How do you actually solve using smart numbers? When I did it, all of my answers were y=0, x=2.

Let's pick x=2, when this is plugged into the equation we get y=0. So we're going to plug in 2 for all x's that we see, when y = 0 that is our answer.

a. 30y^2=3x^2-12 3(2)^2-12 = 0, therefore y=0 when x=2

b. 20y^2=(2x-4)(x+2) (2(2)-4)(2+2) = 0, therefore y=0 when x=2

What am I doing wrong?

I think you are missing out on what the question is asking. It is asking to find the expression that will NOT give you the same value as \(10y^2=(x+2)(x-2)\)

When you do use, y = 0 and x=2, you get the following

A) 15 = 15 B) 10 = 10 C) 9=9 D) 2.5 \(\neq\) 7 E) 0.5 = 0.5

From the original expression you see that when you use y=0 and x=2, you get 0=0 (LHS=RHS).

Thus, with your 'smart numbers', D is the only expression that DOES NOT give you the same values on the left hand side as those on the right hand side. D is thus the correct answer.

FYI, using smart numbers is not the best strategy for this question. You need to realize that \((A+B)(A-B) = A^2-B^2\) and thus the original expression becomes \(10y^2 = x^2-4\)

D will not give you this expression and is thus the correct answer.

Thanks for the response, how are you actually getting for a. 15=15 using x=2, y=0?

30y^2=3x^2-12 30(0)^2 = 3(2)^2 - 12

What is the order of operations? Does the above equal to 0 = 0

Re: Which of the following equations is NOT equivalent to 10y^2= [#permalink]

Show Tags

07 Sep 2015, 19:12

Expert's post

aces021 wrote:

Thanks for the response, how are you actually getting for a. 15=15 using x=2, y=0?

30y^2=3x^2-12 30(0)^2 = 3(2)^2 - 12

What is the order of operations? Does the above equal to 0 = 0

Or does it equal to 30*1 = 36-12 30 = 24 ?

Either way I'm not getting 15=15. Thanks!

Sorry. I had solved this using some other set of values and wrote those values. I have updated the solution. Yes, you are correct that option A will give you y=0 for x=2. As a matter of fact, options A-C and E give y=0 when you use x=2. Option D does not and is thus the correct answer. _________________

To solve this question, we start by FOILing the right hand side of the given equation.

10y^2 = (x+2)(x-2)

10y^2 = x^2 – 4

We will manipulate each of the answer choices to see if it equals 10y^2 = x^2 – 4. Let’s start with A.

A) 30y^2 =3x^2 – 12

If we divide this entire equation by 3 we are left with:

10y^2 = x^2 – 4

Answer choice A is not correct.

B) 20y^2 = (2x-4)(x+2)

FOILing (2x-4)(x+2) we get:

20y^2 = 2x^2 – 8

If we divide this entire equation by 2 we obtain:

10y^2 = x^2 – 4

Answer choice B is not correct.

C) 10y^2 + 4 = x^2

If we subtract 4 from the both sides of the equation, we obtain:

10y^2 = x^2 – 4

Answer choice C is not correct.

D) 5y^2 = x^2 – 2

We should notice that no matter how we try to manipulate 5y^2 = x^2 – 2, it will never be equal to 10y^2 = x^2 – 4. For example, if we multiply both sides of 5y^2 = x^2 – 2 by 2, we will have 10y^2 = 2x^2 – 4. However, that is not the same as 10y^2 = x^2 – 4.

Answer D is correct.

To be certain, we should also test answer E.

E) y^2 = (x^2 – 4)/10

If we multiply the entire equation by 10 we obtain:

10y^2 = x^2 – 4

Answer choice E is not correct.

The answer is D. _________________

Jeffrey Miller Scott Woodbury-Stewart Founder and CEO

gmatclubot

Re: Which of the following equations is NOT equivalent to 10y^2=
[#permalink]
25 May 2016, 09:39

Part 2 of the GMAT: How I tackled the GMAT and improved a disappointing score Apologies for the month gap. I went on vacation and had to finish up a...

Cal Newport is a computer science professor at GeorgeTown University, author, blogger and is obsessed with productivity. He writes on this topic in his popular Study Hacks blog. I was...

So the last couple of weeks have seen a flurry of discussion in our MBA class Whatsapp group around Brexit, the referendum and currency exchange. Most of us believed...