Author 
Message 
TAGS:

Hide Tags

Senior Manager
Status: Math is psychological
Joined: 07 Apr 2014
Posts: 402
Location: Netherlands
GMAT Date: 02112015
WE: Psychology and Counseling (Other)

Re: If a+b=ab, then a*b must be equal to:
[#permalink]
Show Tags
05 Jan 2015, 06:49
I am not sure if the way I thought of the absolute value was correct, but here it is.
QUESTION: If a+b=ab, then a*b must be equal to:
I thought that when there is an absolute value, we think of the "value" within it with no regards to the sign. So, I thought it could be: a+b= ab. If we move a to the other side, both a's get cancelled, which leads to b=b. Moving b to the other side it becomes 2b=0. So, b=0, which means that a*b must be equal to 0.



Math Expert
Joined: 02 Sep 2009
Posts: 58472

Re: If a+b=ab, then a*b must be equal to:
[#permalink]
Show Tags
05 Jan 2015, 07:07
pacifist85 wrote: I am not sure if the way I thought of the absolute value was correct, but here it is.
QUESTION: If a+b=ab, then a*b must be equal to:
I thought that when there is an absolute value, we think of the "value" within it with no regards to the sign. So, I thought it could be: a+b= ab. If we move a to the other side, both a's get cancelled, which leads to b=b. Moving b to the other side it becomes 2b=0. So, b=0, which means that a*b must be equal to 0. You are missing the second case there. If a+b and ab have the same sign, then we'd have a+b = ab > b=0 > ab=0; If a+b and ab have the opposite signs, then we'd have a+b = (ab) > a=0 > ab=0.
_________________



Senior Manager
Status: Math is psychological
Joined: 07 Apr 2014
Posts: 402
Location: Netherlands
GMAT Date: 02112015
WE: Psychology and Counseling (Other)

Re: If a+b=ab, then a*b must be equal to:
[#permalink]
Show Tags
05 Jan 2015, 07:39
Thank you for explaining. I have gone through the absolute values, but they keep creating some confusion.



IIMA, IIMC School Moderator
Joined: 04 Sep 2016
Posts: 1366
Location: India
WE: Engineering (Other)

Re: If a+b=ab, then a*b must be equal to:
[#permalink]
Show Tags
27 Mar 2018, 08:08
Quote: If a+b=ab, then a*b must be equal to:
A. 1 B. 1 C. 0 D. 2 E. 2 niks18 Bunuel chetan2u pushpitkcLet me know if below approach is correct: a+b or ab will always yield a positive value. This is because a modulus always represents an ABSOLUTE distance from number line.So a+b=ab simplifies to a + b = a  b I can cancel a from both sides in all circumstances.2b = 0 > b = 0 or a*b = 0 Hope assumptions made by me are correct.
_________________
It's the journey that brings us happiness not the destination. Feeling stressed, you are not alone!!



Math Expert
Joined: 02 Aug 2009
Posts: 8025

If a+b=ab, then a*b must be equal to:
[#permalink]
Show Tags
27 Mar 2018, 08:40
adkikani wrote: Quote: If a+b=ab, then a*b must be equal to:
A. 1 B. 1 C. 0 D. 2 E. 2 niks18 Bunuel chetan2u pushpitkcLet me know if below approach is correct: a+b or ab will always yield a positive value. This is because a modulus always represents an ABSOLUTE distance from number line.So a+b=ab simplifies to a + b = a  b I can cancel a from both sides in all circumstances.2b = 0 > b = 0 or a*b = 0 Hope assumptions made by me are correct. Ans here will be either A or B or both are 0.. And this is why.. You cannot remove modulus this way, you do know if B is greater or A or they are NEGATIVE.. So square both sides, since both are modulus.. a^2+b^2+2ab=a^2+b^22ab..... 4ab=0.. So either A or B or both are 0
_________________



IIMA, IIMC School Moderator
Joined: 04 Sep 2016
Posts: 1366
Location: India
WE: Engineering (Other)

Re: If a+b=ab, then a*b must be equal to:
[#permalink]
Show Tags
27 Mar 2018, 08:46
chetan2u Quote: You cannot remove modulus this way, you do know if B is greater or A or they are NEGATIVE. But we shall still always get END RESULT as positive on opening modulus. 5 = 5  5 =  (5) = 5 Am I correct?
_________________
It's the journey that brings us happiness not the destination. Feeling stressed, you are not alone!!



Math Expert
Joined: 02 Aug 2009
Posts: 8025

Re: If a+b=ab, then a*b must be equal to:
[#permalink]
Show Tags
27 Mar 2018, 09:13
adkikani wrote: chetan2u Quote: You cannot remove modulus this way, you do know if B is greater or A or they are NEGATIVE. But we shall still always get END RESULT as positive on opening modulus. 5 = 5  5 =  (5) = 5 Am I correct? Yes you are correct.. But 53=35 does not mean 53=35... That is 2=2?? So square the MODULUS to get rid of Modulus
_________________



NonHuman User
Joined: 09 Sep 2013
Posts: 13418

Re: If a+b=ab, then a*b must be equal to:
[#permalink]
Show Tags
21 Apr 2019, 06:50
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=ab, then a*b must be equal to:
[#permalink]
21 Apr 2019, 06:50



Go to page
Previous
1 2
[ 28 posts ]



