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:

Official Answer and Stats are available only to registered users. Register/Login.

_________________

Encourage me by pressing the KUDOS if you find my post to be helpful.

Help me win "The One Thing You Wish You Knew - GMAT Club Contest" http://gmatclub.com/forum/the-one-thing-you-wish-you-knew-gmat-club-contest-140358.html#p1130989

We know that if \((a-b)*c<0\) , either \(c<0\) or \((a-b)<0\) which means \(a<b\)

1. \(a<b\) true. 2. \(c<0\) true. 3. \(|c|<1\) Could be true since \(c\) could be \(-ve\) or \(+ve\). 4. \(ac>bc\) Now if \((a-b)\) is \(+ve\) then \(a>b\) but at the same time \(c\) is \(-ve\) so \(ac\) is less than \(bc\). On the other hand if \((a-b)\) is \(-ve\) than \(a<b\) and \(ac\) cannot be greater than \(bc\) since \(c\) is \(+ve\). 5. \(a^2-b^2>0\) Now from the original statement if \(c<0\) then \((a-b)>0\) so \(a>b\) and \(a^2\) and \(b^2\) are both \(+ve\) so this could be possible.

Hence Answer D
_________________

"Nowadays, people know the price of everything, and the value of nothing."Oscar Wilde

If (a – b)c < 0, which of the following cannot be true?

A. a < b B. c < 0 C. |c| < 1 D. ac > bc E. a^2 – b^2 > 0

Time saving approach:

Given: \((a-b)c<0\).

Now, since only option D has all three unknowns in it, I'd analyze this answer choice first:

D. \(ac > bc\) --> \(ac-bc>0\) --> \((a-b)c>0\). As you can see this option says directly opposite of what is given in the stem, hence it must be false.

There is no need even to check other options, as you cannot have two correct answers.

Answer: D.

P.S. Having all three unknowns does not mean that D is automatically a correct answer. An option could have two or even one unknown and still be a correct answer. For example if one of the options were \(c=0\) or \(a-b=0\) (a=b) then it would mean that it's false, since in this case \((a-b)c=0\), which means that this option would have been a correct answer.

Re: If (a – b)c < 0, which of the following cannot be true? [#permalink]

Show Tags

29 Jan 2014, 09:17

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.
_________________

Re: If (a – b)c < 0, which of the following cannot be true? [#permalink]

Show Tags

14 Feb 2015, 00:35

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.
_________________

Since this question asks which of the following CANNOT be true, you will likely be able to disprove most (if not all) of the wrong answers with some simple examples. If we can prove that an answer IS possible (even just once), then we can eliminate it.

We're told that (A-B)(C) < 0

This means that one of the two parentheses MUST be POSITIVE while the other MUST be NEGATIVE. Recognizing THIS Number Property should speed you up - You can now either TEST VALUES or use this Number Property to eliminate answers.

Answer A: A < B

If A<B, then (A-B) is negative and C is positive. This IS possible. Eliminate A.

Answer B: C < 0

IF C<0, then (A-B) is positive. This IS possible. Eliminate B.

Answer C: |C| < 1

C can be positive or negative, so (A-B) would be the opposite. This IS possible. Eliminate C.

Between the remaining two answers, Answer E seems like the easier option to eliminate....

Answer E: A^2 - B^2 > 0

IF A>B and they're both positive, then (A-B) is positive and C is negative. This IS possible. Eliminate E.

Re: If (a – b)c < 0, which of the following cannot be true? [#permalink]

Show Tags

12 Nov 2016, 08:05

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.
_________________

There’s something in Pacific North West that you cannot find anywhere else. The atmosphere and scenic nature are next to none, with mountains on one side and ocean on...

This month I got selected by Stanford GSB to be included in “Best & Brightest, Class of 2017” by Poets & Quants. Besides feeling honored for being part of...

Joe Navarro is an ex FBI agent who was a founding member of the FBI’s Behavioural Analysis Program. He was a body language expert who he used his ability to successfully...