BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Simple DS problem gone bad

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Junior | Next Rank: 30 Posts
Posts: 24
Joined: Thu Dec 23, 2010 11:13 pm
Location: India
GMAT Score:640

Simple DS problem gone bad

by nk_81 » Fri Dec 31, 2010 6:15 am
John is 'j' years old and Keith is 'k' years old.... and both are atleast 1 year old. is j > k?

1) jk = 2j

2) j + k = 2j

Now KAPLAN says on B is sufficient. Their reasoning is , if we consider equation 1 jk=2j, canceling out j would give us k=2, and thus there is only the value of 'k' and no value of 'j'. Hence INSUFFICIENT.

HOW?

My logic tells me... correct me if I am wrong. since k=2, the only way jk=2j with k=2 is when j=1. Hence the answer to " j>k " is NO

Am I right or am i losing it???? it seems a pretty straight forward answer that I got wrong.
NK
Top
Source: — Data Sufficiency |
User avatar
Legendary Member
Posts: 543
Joined: Tue Jun 15, 2010 7:01 pm
Thanked: 147 times
Followed by:3 members

by anshumishra » Fri Dec 31, 2010 6:30 am
nk_81 wrote:John is 'j' years old and Keith is 'k' years old.... and both are atleast 1 year old. is j > k?

1) jk = 2j

2) j + k = 2j

Now KAPLAN says on B is sufficient. Their reasoning is , if we consider equation 1 jk=2j, canceling out j would give us k=2, and thus there is only the value of 'k' and no value of 'j'. Hence INSUFFICIENT.

HOW?

My logic tells me... correct me if I am wrong. since k=2, the only way jk=2j with k=2 is when j=1. Hence the answer to " j>k " is NO

Am I right or am i losing it???? it seems a pretty straight forward answer that I got wrong.
Question : j>k ?

Statement 1:
jk = 2j => k=2 (j,k!=0)
Insufficient, as no info about j

Statement 2:
j+k = 2j
=> k = j => sufficient (As we can conclusively say that j is not greater than k)

Hence B.
Thanks
Anshu

(Every mistake is a lesson learned )
Top
User avatar
Junior | Next Rank: 30 Posts
Posts: 24
Joined: Thu Dec 23, 2010 11:13 pm
Location: India
GMAT Score:640

by nk_81 » Fri Dec 31, 2010 6:41 am
Hi Anshu,

Can you elaborate on that please. In words if possible.

Dint get this......j,k!=0 ???

Thanks
Naveen
NK
Top
User avatar
Legendary Member
Posts: 543
Joined: Tue Jun 15, 2010 7:01 pm
Thanked: 147 times
Followed by:3 members

by anshumishra » Fri Dec 31, 2010 6:57 am
nk_81 wrote:Hi Anshu,

Can you elaborate on that please. In words if possible.

Dint get this......j,k!=0 ???

Thanks
Naveen
Naveen, can you quote what you didn't get exactly, I'll try to explain that part.
Dint get this......j,k!=0 ???
The equation : jk = 2j
=> j*(k-2) = 0,
Now either J = 0 or k-2
But the question has mentioned both are atleast 1 year old. So that means j != 0
Hence k= 2.
Thanks
Anshu

(Every mistake is a lesson learned )
Top
User avatar
Junior | Next Rank: 30 Posts
Posts: 24
Joined: Thu Dec 23, 2010 11:13 pm
Location: India
GMAT Score:640

by nk_81 » Fri Dec 31, 2010 7:08 am
Anshu,

How much ever I try to wrap my head around it... for some reason I am unable to comprehend why this can't be the case.

I am putting the value back in the equation it was derived from, that seems strange to me as well and in the process ...

j*k=2*j ; k=2; for k to be equal to 2 since the equation jk=2j is true, j has to be 1...since 2 times j = 2j....does that make sense?
NK
Top
User avatar
Legendary Member
Posts: 543
Joined: Tue Jun 15, 2010 7:01 pm
Thanked: 147 times
Followed by:3 members

by anshumishra » Fri Dec 31, 2010 7:16 am
nk_81 wrote:Anshu,

How much ever I try to wrap my head around it... for some reason I am unable to comprehend why this can't be the case.

I am putting the value back in the equation it was derived from, that seems strange to me as well and in the process ...

j*k=2*j ; k=2; for k to be equal to 2 since the equation jk=2j is true, j has to be 1...since 2 times j = 2j....does that make sense?

j*k=2*j ; k=2; for k to be equal to 2 since the equation jk=2j is true, j has to be 1
Lets check with few values.
j=1,k=2
j*k = 1*2 = 2 and 2*j = 2*1 = 2
j=2,k=2
j*k = 2*2 = 4 and 2*j = 2*2 = 4
j=3, k=2
j*k = 3*2 = 6 and 2*j = 2*3 = 6

So, you can see for any value of j the equation holds.
Thanks
Anshu

(Every mistake is a lesson learned )
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3380
Joined: Mon Mar 03, 2008 1:20 am
Thanked: 2256 times
Followed by:1535 members
GMAT Score:800

by lunarpower » Sun Jan 02, 2011 12:29 am
you can divide both sides of any equation by any quantity that is known to be nonzero. (with inequalities, you have to be more careful -- you can't divide both sides by a quantity unless it is known to be nonzero and its sign is known, unless you split the result into cases according to the unknown sign.)

so, since j is not 0:
jk = 2j
divide by j
--> k = 2.
no information about j.

--

re: your confusion about the other post, that poster was using the symbol "!=" as a substitute for "≠".
this is accepted notation in formal logic classes, but it's still sort of weird on a forum (especially because, in certain contexts, it can be misinterpreted as a factorial).

TO EVERYONE
if you don't know how to type "≠", just open up a search engine, type in "not equal sign", and then copy and paste from one of the zillions of results that show up.
the same goes for ">" and "<" -- either google/copy/paste or just use normal "<" and ">" with the underline enabled. that makes first a lot more readable than they are if you use ">=" or "<=", the latter of which looks like an arrow.
Ron has been teaching various standardized tests for 20 years.

--

Pueden hacerle preguntas a Ron en castellano
Potete chiedere domande a Ron in italiano
On peut poser des questions à Ron en français
Voit esittää kysymyksiä Ron:lle myös suomeksi

--

Quand on se sent bien dans un vêtement, tout peut arriver. Un bon vêtement, c'est un passeport pour le bonheur.

Yves Saint-Laurent

--

Learn more about ron
Top
User avatar
Legendary Member
Posts: 543
Joined: Tue Jun 15, 2010 7:01 pm
Thanked: 147 times
Followed by:3 members

by anshumishra » Sun Jan 02, 2011 6:19 am
lunarpower wrote: re: your confusion about the other post, that poster was using the symbol "!=" as a substitute for "≠".
this is accepted notation in formal logic classes, but it's still sort of weird on a forum (especially because, in certain contexts, it can be misinterpreted as a factorial).

TO EVERYONE
if you don't know how to type "≠", just open up a search engine, type in "not equal sign", and then copy and paste from one of the zillions of results that show up.
the same goes for ">" and "<" -- either google/copy/paste or just use normal "<" and ">" with the underline enabled. that makes first a lot more readable than they are if you use ">=" or "<=", the latter of which looks like an arrow.
lunarpower,

You are right. I used "!=" as a substitute for "≠". In my future posts I'll use the other notation. Thanks for pointing that out, as I myself in many cases have used "!" as factorial notation.
Thanks
Anshu

(Every mistake is a lesson learned )
Top
Post new topic Post Reply
• Page 1 of 1