Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 59083

If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
25 Jun 2015, 03:30
Question Stats:
88% (00:51) correct 12% (00:56) wrong based on 195 sessions
HideShow timer Statistics
If ab > 0, which of the following must be negative? (A) a + b (B) a + b (C) b  a (D) a/b (E) a/b Kudos for a correct solution.
Official Answer and Stats are available only to registered users. Register/ Login.
_________________



CEO
Status: GMATINSIGHT Tutor
Joined: 08 Jul 2010
Posts: 2977
Location: India
GMAT: INSIGHT
WE: Education (Education)

If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
25 Jun 2015, 03:40
Bunuel wrote: If ab > 0, which of the following must be negative?
(A) a + b (B) a + b (C) b  a (D) a/b (E) a/b
Kudos for a correct solution. If ab > 0 the we Infer that a and b both have same sign i.e. either both a and b are Positive or Both a and b are NegativeNow Checking Options:(A) a + b will be positive for both a and b to be positive hence INCORRECT OPTION(B) a + b will be positive for both a and b to be positive hence INCORRECT OPTION(C) b  a May be positive for both a and b to be positive (e.g. b=3 and a=2) henceINCORRECT OPTION(D) a/b will be positive for both a and b to be positive or Negative hence INCORRECT OPTION(E) a/b will always be Negative because an and b have same sign so a/b will be positive therefore a/b will be Negative hence CORRECTAnswer: Option
_________________
Prosper!!!GMATinsightBhoopendra Singh and Dr.Sushma Jha email: info@GMATinsight.com I Call us : +919999687183 / 9891333772 Online OneonOne Skype based classes and Classroom Coaching in South and West Delhihttp://www.GMATinsight.com/testimonials.htmlACCESS FREE GMAT TESTS HERE:22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 15454
Location: United States (CA)

Re: If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
25 Jun 2015, 18:37
Hi All, These types of questions are perfect for TESTing VALUES. Since the question asks which of the following MUST be NEGATIVE, if an answer can EVER be positive then you can eliminate it immediately. We're told that AB > 0. We're asked which of the 5 answers MUST be NEGATIVE... IF.... A = 2 B = 3 Answer A: 2+3 = 5 NOT a match Answer B: 2 + 3 = 5 NOT a match Answer C: 32 = 1 NOT a match Answer D: 2/3 = NOT a match There's only one answer left.... Answer E: 2/3 = This IS a match Final Answer: GMAT assassins aren't born, they're made, Rich
_________________
Contact Rich at: Rich.C@empowergmat.comThe Course Used By GMAT Club Moderators To Earn 750+ souvik101990 Score: 760 Q50 V42 ★★★★★ ENGRTOMBA2018 Score: 750 Q49 V44 ★★★★★



Math Expert
Joined: 02 Aug 2009
Posts: 8176

Re: If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
25 Jun 2015, 20:59
Bunuel wrote: If ab > 0, which of the following must be negative?
(A) a + b (B) a + b (C) b  a (D) a/b (E) a/b
Kudos for a correct solution. Hi, many of us have solved this with picking values.. But it is very important to look at the answer and pick up number .... There may be many instances where the number picked up may give us a wrong answer and we may have two or three answer left .. we may have to again start with POE in remaining choices, although eventually we will come to correct answer after some more steps... I feel if we know properties of number , we can easily get to the answer... in this particular Q, we have both the numbers of same sign.. Therefore any addition, subtraction can give you any answer depending on the values we take... However multiplication , division and sum of modulus of the numbers(i donot think GMAT will test us in more complicated issues) will always be the ones closer to the answer.. Here the division will always be positive if the fraction is positive ..., But will be ive if there is a ive sign in front Or in other words it will take sign that is in front of fraction... hence E will be correct..
_________________



Retired Moderator
Joined: 29 Apr 2015
Posts: 818
Location: Switzerland
Concentration: Economics, Finance
WE: Asset Management (Investment Banking)

Re: If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
25 Jun 2015, 06:04
Bunuel wrote: If ab > 0, which of the following must be negative?
(A) a + b (B) a + b (C) b  a (D) a/b (E) a/b
Kudos for a correct solution. ab > 0 implies that ab have the same sign. Either both are positive or negative. Pick 4 Numbers for a and b respectively. Two positives a = 10 and b = 5 and two negatives a = 10 b = 5. Plug in and POE as soon you find any non negative result. E will always be negative.
_________________
Saving was yesterday, heat up the gmatclub.forum's sentiment by spending KUDOS!
PS Please send me PM if I do not respond to your question within 24 hours.



Math Expert
Joined: 02 Aug 2009
Posts: 8176

Re: If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
25 Jun 2015, 20:49
reto wrote: Bunuel wrote: If ab > 0, which of the following must be negative?
(A) a + b (B) a + b (C) b  a (D) a/b (E) a/b
Kudos for a correct solution. ab > 0 implies that ab have the same sign. Either both are positive or negative. Pick 4 Numbers for a and b respectively. Two positives a = 10 and b = 5 and two negatives a = 10 b = 5. Plug in and POE as soon you find any non negative result. E will always be negative. Hi, if there would have been an answer choice blal.., your chosen numbers will give you negative results...
_________________



Math Expert
Joined: 02 Sep 2009
Posts: 59083

Re: If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
29 Jun 2015, 06:03
Bunuel wrote: If ab > 0, which of the following must be negative?
(A) a + b (B) a + b (C) b  a (D) a/b (E) a/b
Kudos for a correct solution. MANHATTAN GMAT OFFICIAL SOLUTION:You might solve this problem a different way, but let’s see how a chart would work. First, you need to figure out the possible signs of a and b that match the constraint ab> 0: Attachment:
20150629_1659.png [ 9.14 KiB  Viewed 4245 times ]
There are two scenarios that match: either a and b are both positive or they are both negative. That is, a and b have the same sign. Now test the answer choices. (A) a + b: If a and b are both positive, then a + b will be positive. Eliminate (A). (B) a + b: a will always be positive. If b is positive, a  + b will be positive. Eliminate (B). (C) b  a: If a and b are both positive, b  a could be either positive or negative. If b is 6 and a is 3, 6  3 = 3, which is positive. Eliminate (C). (D) a/b: If a and b are both positive, a/b will be positive. Eliminate (D) (E) a/b. If a and b are both positive, a/b will be negative. If a and b are both negative, a/b will still be negative. (E) is the correct answer.
_________________



SVP
Joined: 06 Nov 2014
Posts: 1871

Re: If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
01 Jul 2015, 00:51
If ab > 0, which of the following must be negative? If the product of a and b is positive, a and b must have the same sign (either both positive or both negative). Therefore we're looking for the answer choice for which a and b will (with certainty) have opposite signs. E is the only option. (A) a + b (B) a + b (C) b  a (D) a/b (E) a/b



Retired Moderator
Joined: 19 Mar 2014
Posts: 917
Location: India
Concentration: Finance, Entrepreneurship
GPA: 3.5

Re: If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
21 Jun 2017, 15:57
If ab > 0, which of the following must be negative? This means a & b have same signs. (A) a + b =====> Positive(B) a + b =====> Positive(C) b  a =====> Positive(D) a/b =====> Positive(E) a/b =====> NegativeExcept for option E, where the value will always be negative, all other options can have positive values. Hence, Answer is E
_________________
"Nothing in this world can take the place of persistence. Talent will not: nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not: the world is full of educated derelicts. Persistence and determination alone are omnipotent."
Best AWA Template: https://gmatclub.com/forum/howtoget60awamyguide64327.html#p470475



Senior Manager
Joined: 24 Oct 2016
Posts: 250
Location: India
Concentration: Finance, International Business
GPA: 3.96
WE: Human Resources (Retail Banking)

Re: If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
22 Jun 2017, 05:04
whenever we see which of the following ,then always start with option E , most of times the answer is hidden at the last option which is commonly used by GMAT to waste the time of aspirant . we see that ab>0 then a or b must be ve or +ve so only E states that it will be ve in all cases . hence E



Target Test Prep Representative
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2812

Re: If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
24 Jun 2017, 08:33
Bunuel wrote: If ab > 0, which of the following must be negative?
(A) a + b (B) a + b (C) b  a (D) a/b (E) a/b Since ab is greater than zero, a and b are either both positive or both negative. Scanning our answer choices, we see that a/b must be negative. For example, if a and b are both positive, then a/b is a negative divided by a positive, which results in a negative quotient. If a and b are both negative, then a/b is a positive divided by a negative, which also results in a negative quotient. Answer: E
_________________
5star rated online GMAT quant self study course See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews
If you find one of my posts helpful, please take a moment to click on the "Kudos" button.



VP
Joined: 31 Oct 2013
Posts: 1471
Concentration: Accounting, Finance
GPA: 3.68
WE: Analyst (Accounting)

Re: If ab > 0, which of the following must be negative?
[#permalink]
Show Tags
21 Feb 2019, 16:06
Bunuel wrote: If ab > 0, which of the following must be negative?
(A) a + b (B) a + b (C) b  a (D) a/b (E) a/b
Kudos for a correct solution. ab>0 Thus , both a and b are positive or both are negative. Option E)  a/b a/b >0 , As both a and b have the same sign. When we multiply positive result of a/b by a negative sign. Ultimate result will be negative. E is the correct answer.




Re: If ab > 0, which of the following must be negative?
[#permalink]
21 Feb 2019, 16:06






