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:

Hi guys, this was written before I saw the post on how to write mathematically correct in the forum.

DS #90:

My question about this problem has to do with part 1. The question is fairly simple: Why in part 1 can’t I make all signs match up and equal x? x/yz would then look like this in the way I did it: x / 2x*2x/5.

Here is what the book says:

(1) From this, z can be expressed in terms of y by substituting y/2 for x in the equation z=2x/5, which gives us z=2(2/5) / 5= y/5. The value of x/yz in terms of y is then y/2 / y(y/5) = y/2(5/y[squared])=5/2y. This expression cannot be evaluated further since no information is given about the value of y; not sufficient. (BCE).

Here is how I did it:

What I did is take x=y/2 and make it 2x=y (which Quant book did not do), which then gave me: x / 2x*2x/5, which gave me x / 4x/5, which equals 5x / 4x, and I get 5/4. Meaning I mark this as AD and move to part 2.

Part 2 is easier to solve because we just plug in: y=10, x=5, z=2. 5/10*2=1/4, for which I pick letter D as my answer because both solutions by them selves are sufficient.

One of the big problems I see with my answer is that in part 1 I got 5/4, and in part 2 I got ¼, which is a contradiction and according to MGMAT, I did something wrong.

Please explain this problem and let me know whether and if so, then why I am wrong.

Hi guys, this was written before I saw the post on how to write mathematically correct in the forum.

DS #90:

What is the value of x / yz ?

1. x=y/2 and z=2x/5 2. x/z=5/2 and 1/y=1/10

My question about this problem has to do with part 1. The question is fairly simple: Why in part 1 can’t I make all signs match up and equal x? x/yz would then look like this in the way I did it: x / 2x*2x/5.

Here is what the book says:

(1) From this, z can be expressed in terms of y by substituting y/2 for x in the equation z=2x/5, which gives us z=2(2/5) / 5= y/5. The value of x/yz in terms of y is then y/2 / y(y/5) = y/2(5/y[squared])=5/2y. This expression cannot be evaluated further since no information is given about the value of y; not sufficient. (BCE).

Here is how I did it:

What I did is take x=y/2 and make it 2x=y (which Quant book did not do), which then gave me: x / 2x*2x/5, which gave me x / 4x/5, which equals 5x / 4x, and I get 5/4. Meaning I mark this as AD and move to part 2.

Part 2 is easier to solve because we just plug in: y=10, x=5, z=2. 5/10*2=1/4, for which I pick letter D as my answer because both solutions by them selves are sufficient.

One of the big problems I see with my answer is that in part 1 I got 5/4, and in part 2 I got ¼, which is a contradiction and according to MGMAT, I did something wrong.

Please explain this problem and let me know whether and if so, then why I am wrong.

My question about this problem has to do with part 1. The question is fairly simple: Why in part 1 can’t I make all signs match up and equal x? x/yz would then look like this in the way I did it: x / 2x*2x/5.

Here is what the book says:

(1) From this, z can be expressed in terms of y by substituting y/2 for x in the equation z=2x/5, which gives us z=2(2/5) / 5= y/5. The value of x/yz in terms of y is then y/2 / y(y/5) = y/2(5/y[squared])=5/2y. This expression cannot be evaluated further since no information is given about the value of y; not sufficient. (BCE).

Hi Bunuel/Instructors, I have a doubt : (In red above) how can we cancel Y in numerator with Y in denominator, if the problem doesnt states: y IS NOT= 0. As the cancellation of Y(or for any variable) involves/multiplication or division by Y on both ends.

So far as I understand GMAT has marked statements in many DS Qs as insuffiecient on this ground stating "we cant divide by a variable unless it is mentioned as non zero"

I observed similar things in Q57(where m/n = 5/3 has been cross multiplied to 5n =3m) - they ignored the point that if m or n is 0 then the answer B wont be SUFFICIENT.

& Q15(in option B, they have ignored the case of x=0, which if true makes B not sufficient as it also the solution also involves division by a variable )

ARE there any particular scenarios in which we are allowed to divide/multiply varibles or transfer them by cross multiplication in an equation. OR where am i lacking in my basics ?

My question about this problem has to do with part 1. The question is fairly simple: Why in part 1 can’t I make all signs match up and equal x? x/yz would then look like this in the way I did it: x / 2x*2x/5.

Here is what the book says:

(1) From this, z can be expressed in terms of y by substituting y/2 for x in the equation z=2x/5, which gives us z=2(2/5) / 5= y/5. The value of x/yz in terms of y is then y/2 / y(y/5) = y/2(5/y[squared])=5/2y. This expression cannot be evaluated further since no information is given about the value of y; not sufficient. (BCE).

Hi Bunuel/Instructors, I have a doubt : (In red above) how can we cancel Y in numerator with Y in denominator, if the problem doesnt states: y IS NOT= 0. As the cancellation of Y(or for any variable) involves/multiplication or division by Y on both ends.

So far as I understand GMAT has marked statements in many DS Qs as insuffiecient on this ground stating "we cant divide by a variable unless it is mentioned as non zero"

I observed similar things in Q57(where m/n = 5/3 has been cross multiplied to 5n =3m) - they ignored the point that if m or n is 0 then the answer B wont be SUFFICIENT.

& Q15(in option B, they have ignored the case of x=0, which if true makes B not sufficient as it also the solution also involves division by a variable )

ARE there any particular scenarios in which we are allowed to divide/multiply varibles or transfer them by cross multiplication in an equation. OR where am i lacking in my basics ?

Please help !!

What is the value of x/yz?

(1) \(x = \frac{y}{2}\) and \(z = \frac{2x}{5}\). If \(y=10\), then \(x=5\), \(z=2\) and in this case \(\frac{x}{yz}=\frac{5}{20}=\frac{1}{4}\) BUT if \(y=20\), then \(x=10\), \(z=4\) and in this case \(\frac{x}{yz}=\frac{10}{80}=\frac{1}{8}\). Not sufficient.

(2) \(\frac{x}{z} = \frac{5}{2}\) and \(\frac{1}{y} = \frac{1}{10}\). Multiply these two equations: \(\frac{x}{yz}=\frac{5}{20}\). Sufficient.

Answer: B.

As for your questions: 1. Yes, it would be better if the stem stated that \(yz\neq{0}\). If you don't state that, then x=y=z=0 satisfies the first statement and in this case x/(yz) is undefined.

2. As for m/n = 5/3. This equation already implies that neither of them is zero: if m=0, then m/n = 0 and not 5/3 and if n=0, then m/n is not defined, and not 5/3. So, in this case we can write 3m = 5n.

As for your questions: 1. Yes, it would be better if the stem stated that \(yz\neq{0}\). If you don't state that, then x=y=z=0 satisfies the first statement and in this case x/(yz) is undefined.

I think you understand my doubt. The scenarios(x,y,z=0) will make the solution undefined. Hence answer E. (Thats the way i solved, considering all scenarios) SO why are we not picking these values as well? The statement is meant to be true for all real numbers ~ RIGHT ? How to decide between option D(here) & option E for such questions in exam. Seeking lessons from your experience

Bunuel wrote:

3. I don't know what question is Q15.

It is question 15 from Data sufficiency & Q57 is question 57.

As for your questions: 1. Yes, it would be better if the stem stated that \(yz\neq{0}\). If you don't state that, then x=y=z=0 satisfies the first statement and in this case x/(yz) is undefined.

I think you understand my doubt. The scenarios(x,y,z=0) will make the solution undefined. Hence answer E. (Thats the way i solved, considering all scenarios) SO why are we not picking these values as well? The statement is meant to be true for all real numbers ~ RIGHT ? How to decide between option D(here) & option E for such questions in exam. Seeking lessons from your experience

Bunuel wrote:

3. I don't know what question is Q15.

It is question 15 from Data sufficiency & Q57 is question 57.

The answer to the question is neither D nor E, it's B.

(1) is not sufficient irrespective whether you have \(yz\neq{0}\) condition or not. The point is that, their solution for (1) is not 100% correct since it's not mentioned that \(yz\neq{0}\).

(2) is still sufficient as shown in my post above.

As for Q15 and Q57: I don't know what questions are you talking about. Please post them.
_________________

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.
_________________

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.
_________________

Version 8.1 of the WordPress for Android app is now available, with some great enhancements to publishing: background media uploading. Adding images to a post or page? Now...

Post today is short and sweet for my MBA batchmates! We survived Foundations term, and tomorrow's the start of our Term 1! I'm sharing my pre-MBA notes...

“Keep your head down, and work hard. Don’t attract any attention. You should be grateful to be here.” Why do we keep quiet? Being an immigrant is a constant...