It is currently 28 Jun 2017, 23:15

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

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

is there a quick way to solve this

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Intern
Intern
avatar
Joined: 30 May 2008
Posts: 4
is there a quick way to solve this [#permalink]

Show Tags

New post 11 Dec 2010, 16:35
What is X?

(480/x) = (480/x+16) + 5

To get rid of the x as denomintor, I was thinking of multyiplying the numerator with (x)(x+16) but it seems convulted and long for a gmat problem...any shortcuts..

Thanks!
Kaplan GMAT Instructor
User avatar
Joined: 21 Jun 2010
Posts: 147
Location: Toronto
Re: is there a quick way to solve this [#permalink]

Show Tags

New post 11 Dec 2010, 18:20
sudimba wrote:
What is X?

(480/x) = (480/x+16) + 5

To get rid of the x as denomintor, I was thinking of multyiplying the numerator with (x)(x+16) but it seems convulted and long for a gmat problem...any shortcuts..

Thanks!


Hi!

Do you have answer choices? Almost certainly the quickest way to get the right answer is to backsolve.

You could also work it out intiutively - we know that 480/x is 5 more than 480/(x+16). So, what factor pairs of 480 have one number that's 5 apart and another that's 16 apart?

1 480
2 240
3 160
4 120
5 96
6 80
8 60
10 48
12 40
15 32
16 30
20 24

the only pairs that match are 10*48 and 15*32 (x=32, x+16=48; 480/32 = 15 which is 5 more than 480/48 = 10).

So, x=32.
Manager
Manager
avatar
Joined: 24 Nov 2010
Posts: 211
Location: United States (CA)
Concentration: Technology, Entrepreneurship
Schools: Ross '15, Duke '15
GMAT ToolKit User
Re: is there a quick way to solve this [#permalink]

Show Tags

New post 11 Dec 2010, 19:47
sudimba wrote:
What is X?

(480/x) = (480/x+16) + 5

To get rid of the x as denomintor, I was thinking of multyiplying the numerator with (x)(x+16) but it seems convulted and long for a gmat problem...any shortcuts..

Thanks!


480/x = 480/(x+16) + 5
=> 96/x = 96/(x+16) +1 (div. entire eqn by 5)
=> 96x+96*16 = 96x +x2 +16x
=> x2 + 16x - 96*16 = 0 (Also, 96*16 = 48*2*16 = 48*32, And 48-32=16)
=> x2 + 48x - 32x - 48*32 =0
=> x= (-48, 32)

note: x2 = "x squared"

i think it can be done in 2 mins since we don't have to complete the multiplication of any big numbers.
Expert Post
Veritas Prep GMAT Instructor
User avatar
S
Joined: 16 Oct 2010
Posts: 7450
Location: Pune, India
Re: is there a quick way to solve this [#permalink]

Show Tags

New post 12 Dec 2010, 19:36
sudimba wrote:
What is X?

(480/x) = (480/x+16) + 5

To get rid of the x as denomintor, I was thinking of multyiplying the numerator with (x)(x+16) but it seems convulted and long for a gmat problem...any shortcuts..

Thanks!


\(\frac{480}{x} = \frac{480}{{x+16}} + 5\)
\(\frac{96}{x} = \frac{96}{{x+16}} + 1\)

If there are no options to help out at this stage, consider that numbers in GMAT problems almost always fall beautifully in place.
I will first try x = 16 because I know 16*6 = 96
I get \(\frac{96}{16} = \frac{96}{{16+16}} + 1\)
6=4 (x is not 16)
Since I need to reduce the left hand side, I will try a bigger value of x, 24 because 96/24 = 4 but 24+16 = 40 which doesn't divide 96 completely.
Next number I will try will be 32 since 96/32 = 3. Also 96/(32 + 16) = 2. This satisfies the equation.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199

Veritas Prep Reviews

Re: is there a quick way to solve this   [#permalink] 12 Dec 2010, 19:36
    Similar topics Author Replies Last post
Similar
Topics:
5 Important Math Formula for quick solving of questions tiklimumita 1 25 Apr 2017, 13:08
Experts publish their posts in the topic how to solve 4^4 quick IamWeezel 4 21 Nov 2016, 18:53
Is there an easy way to solve this question? ozzykhan 0 30 Aug 2015, 12:50
1 Experts publish their posts in the topic Most efficient way to solve these equations ? soaringAlone 4 18 Jul 2015, 06:07
78 Quick Way to Graph Inequalities Nach0 30 22 Mar 2017, 19:46
Display posts from previous: Sort by

is there a quick way to solve this

  new topic 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®.