How can we do this quickly? : Quant Question Archive [LOCKED]
Check GMAT Club App Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

It is currently 08 Dec 2016, 19:04
GMAT Club Tests

Close

GMAT Club Daily Prep

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.

Close

Request Expert Reply

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

How can we do this quickly?

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
CIO
CIO
User avatar
Joined: 09 Mar 2003
Posts: 463
Followers: 2

Kudos [?]: 56 [0], given: 0

How can we do this quickly? [#permalink]

Show Tags

New post 25 Aug 2004, 17:32
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Hello everyone.

For years, everyone's been talking about plugging in numbers for algebra problems. You pick a number for the variable, plug it in, get an answer, and then find that answer in the answer choices.

I think this is dangerous, because it only works sometimes, and I think that algebra or some other trick is always important as a backup. Plugging in should be done by people who understand it and when not to use it.

Sorry for waxing on about that, but I ran across a problem today that would be very difficult to plug numbers into, but is also very time consuming using straightforward algebra. You might expect it to work out well with substitution, but you'll see that it doesn't. So I thought I'd post it here and see what everyone thought about it, and if there's some clever thing that I'm not seeing.

--------------
If 2x + 3y = 1, what is (x/2) + (y/3) in terms of y?

A) y/5

B) (1 - 3y)/2

C) (1 - 3y)/4

D) (3y + 4)/15

E) (3 - 5y)/12

Last edited by ian7777 on 25 Aug 2004, 17:56, edited 1 time in total.
Manager
Manager
avatar
Joined: 28 Jun 2004
Posts: 90
Followers: 1

Kudos [?]: 70 [0], given: 0

 [#permalink]

Show Tags

New post 25 Aug 2004, 17:49
I guess I am losing my mind. But for (x/2) + (y/2), I am getting (1-y)/4. This is not an option listed.
GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 07 Jul 2004
Posts: 5062
Location: Singapore
Followers: 30

Kudos [?]: 348 [0], given: 0

 [#permalink]

Show Tags

New post 25 Aug 2004, 17:51
i'm getting (1-y)/4 as well
CIO
CIO
User avatar
Joined: 09 Mar 2003
Posts: 463
Followers: 2

Kudos [?]: 56 [0], given: 0

 [#permalink]

Show Tags

New post 25 Aug 2004, 17:56
Sorry, my bad completely. The question should read,

"...what is (x/2) + (y/3) in terms of y?"

I'll fix the original post.
Senior Manager
Senior Manager
User avatar
Joined: 25 Dec 2003
Posts: 359
Location: India
Followers: 1

Kudos [?]: 37 [0], given: 0

 [#permalink]

Show Tags

New post 25 Aug 2004, 18:00
If 2x + 3y = 1, what is (x/2) + (y/3) in terms of y?

---> 2x+3y=1
---> 2x=1-3y
---> x= (1-3y)/2
---> x/2=(1-3y)/4

Add y/3 on both sides.....

(x/2)+(y/3)= (1-3y)/4 + (y/3)

---> u get (3-5y)/12

(Solved less than one minute) :)
_________________

Giving another SHOT

GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 07 Jul 2004
Posts: 5062
Location: Singapore
Followers: 30

Kudos [?]: 348 [0], given: 0

 [#permalink]

Show Tags

New post 25 Aug 2004, 18:02
(E). 20 secs. I think good old substitution is still very fast in this case. If you note that you'll end up with 2 and 3 as denominator, you can work two steps ahead while substituting by adjusting the integer value of y as you work throuhg the problem.
Director
Director
avatar
Joined: 20 Jul 2004
Posts: 593
Followers: 2

Kudos [?]: 123 [0], given: 0

 [#permalink]

Show Tags

New post 25 Aug 2004, 18:54
I guess solving might be faster than substituting numbers (I mean, if Ian hadn't given the preface).

Let the value be M

2x + 3y = 1
3x + 2y = 6M

Solving this,
-5y = 12M-1
M = (3-5y)/12
Manager
Manager
avatar
Joined: 18 Jun 2004
Posts: 103
Location: san jose , CA
Followers: 2

Kudos [?]: 72 [0], given: 0

 [#permalink]

Show Tags

New post 26 Aug 2004, 07:41
15 seconds , I got it as E .

divide the existing equation by 4 and move 3y/4 to the right side ,
you know x/2 and then simply add y/3 .

x /2 = (1-3y)/4

x/2 + y/3 = (1-3y)/4 + y/12
= (3-5y)/12
_________________

---- Hero never chooses Destiny
Destiny chooses Him ......

Manager
Manager
avatar
Joined: 18 Jun 2004
Posts: 103
Location: san jose , CA
Followers: 2

Kudos [?]: 72 [0], given: 0

 [#permalink]

Show Tags

New post 26 Aug 2004, 07:43
Infact the moment you see the denominator as 12 , you can choose the choice E , because there is no other choice which has denominator 12 .

My bad , if i had not overlooked the choices , i think this problem can be solved with in 15 seconds .
_________________

---- Hero never chooses Destiny
Destiny chooses Him ......

Intern
Intern
avatar
Joined: 22 Mar 2004
Posts: 25
Location: TX
Followers: 0

Kudos [?]: 0 [0], given: 0

 [#permalink]

Show Tags

New post 26 Aug 2004, 07:50
hardworker_indian wrote:
I guess solving might be faster than substituting numbers (I mean, if Ian hadn't given the preface).

Let the value be M

2x + 3y = 1
3x + 2y = 6M

Solving this,
-5y = 12M-1
M = (3-5y)/12

This is probably one of the most straightforward way of solving the equation!
  [#permalink] 26 Aug 2004, 07:50
Display posts from previous: Sort by

How can we do this quickly?

  post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.