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:

Given : a,b,c and d are all non-zero ints.
asked: ab/cd > 0 ?

(1) ad + bc = 0
---------------------
ad = - bc --> one of abcd has a different sign that the others
ex: all +ve and one is -ve or all -ve and one is +ve
So, is ab/cd > 0 ? NO

statement 1 is sufficient

(2) abcd = -4
------------------
abcd = -ve # --> one abcd also has a different sign than the others
So, is ab/cd > 0 ? NO

For non-zero integers a, b, c and d, is ab/cd positive? [#permalink]

Show Tags

03 Aug 2013, 09:26

For non-zero integers a, b, c and d, is ab/cd positive?

(1) ad + bc = 0 (2) abcd = -4

I dont agree with the OA.

IMO B.

Statement 1 : ad = -bc 1) If all integers a,b,c & d are -ve/+ve, then statement 1 holds true and ab/bc is positive. 2) If any one integer is -ve & other 3 integers are positive, statement 1 holds true and ab/bc is negative.

Let me know where my thinking is wrong?

Last edited by Zarrolou on 03 Aug 2013, 09:30, edited 1 time in total.

Re: For non-zero integers a, b, c and d, is ab/cd positive? [#permalink]

Show Tags

03 Aug 2013, 09:34

mohitvarshney wrote:

For non-zero integers a, b, c and d, is ab/cd positive?

(1) ad + bc = 0 (2) abcd = -4

I dont agree with the OA.

IMO B.

Statement 1 : ad = -bc 1) If all integers a,b,c & d are -ve/+ve, then statement 1 holds true and ab/bc is positive. 2) If any one integer is -ve & other 3 integers are positive, statement 1 holds true and ab/bc is negative.

Let me know where my thinking is wrong?

If \(a,b,c,d\) are all positive or negative (1) does not hold true,as \(positive+positive>0\) and \(negative + negative < 0\) ( and not equal 0). Your second point is correct.

Hope it's clear. _________________

It is beyond a doubt that all our knowledge that begins with experience.

Re: For non-zero integers a, b, c and d, is ab/cd positive? [#permalink]

Show Tags

17 Aug 2013, 01:26

1

This post was BOOKMARKED

From statement 1, we know that \(ad+bc=0\) \(=>\) \(ad=-bc\) \(=>\) \(-\frac{a}{b}=\frac{c}{d}\) \(=>\) \(-\frac{a*b}{b*b}=\frac{c*d}{d*d}\) \(=>\) \(-\frac{ab}{b^2}=\frac{cd}{d^2}\) \(=>\) \(\frac{ab}{cd}=-\frac{b^2}{d^2}\) Thus from 1, we come to know that ab/cd is negative since \(b^2\) and \(d^2\) are positive

From statement 2, \(abcd=-4\) Now the only way this can happen is if one of the term is negative. And if one of the term is negative, then ab/cd has to be negative.

Re: For non-zero integers a, b, c and d, is ab/cd positive? [#permalink]

Show Tags

10 Oct 2013, 14:57

1

This post received KUDOS

mm007 wrote:

For non-zero integers a, b, c and d, is ab/cd positive?

(1) ad + bc = 0

(2) abcd = -4

So this question is basically testing negatives and positives (Remember >0).

First Statement

ad = -bc. Now we could rearrange this to be a/c = -b/d. Now replacing in the original statement we would have (-b/d)(b/d) . Since this is basically the same fraction but with different signs then the result HAS to be negative. Therefore this statement is Sufficient

Second Statement

abcd = -4. Now here, we see that the result is -ve. So actually, we can either have 1 negative or 3 negatives. But either choice will give us ab/cd <0. Because the only thing we need is to have an odd number of negative signed numbers. I suggest to try it with different combinations and see it for yourself

Re: For non-zero integers a, b, c and d, is ab/cd positive? [#permalink]

Show Tags

25 Nov 2014, 04:53

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: For non-zero integers a, b, c and d, is ab/cd positive? [#permalink]

Show Tags

10 Nov 2015, 19:49

Q: a, b, c, d are non-zero integers. Is ab/cd positive?

St1: ad + cb = 0, ad = -cb. One of the four elements is of an opposite sign, therefore either one or three elements are negative and ab/cd = -ve. Sufficient.

St2: abcd = -4, ab = -4/cd, ab/cd = -4/cd^2, therefore ab/cd is negative.

gmatclubot

Re: For non-zero integers a, b, c and d, is ab/cd positive?
[#permalink]
10 Nov 2015, 19:49

So, my final tally is in. I applied to three b schools in total this season: INSEAD – admitted MIT Sloan – admitted Wharton – waitlisted and dinged No...

A few weeks ago, the following tweet popped up in my timeline. thanks @Uber_Mumbai for showing me what #daylightrobbery means!I know I have a choice not to use it...

“This elective will be most relevant to learn innovative methodologies in digital marketing in a place which is the origin for major marketing companies.” This was the crux...