It is currently 17 Oct 2017, 12:12

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# I got this correct through backsolving....but didn't get it

Author Message
Senior Manager
Joined: 18 Jun 2007
Posts: 287

Kudos [?]: 61 [0], given: 0

I got this correct through backsolving....but didn't get it [#permalink]

### Show Tags

09 Feb 2008, 14:47
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

### HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

I got this correct through backsolving....but didn't get it through direct method...
Here is what i tried:

(90/v-3) - (90/v+3) = 0.5
= > {90*(v+3)} - {90*(v-3)}/ v^2 - 3^2 = 0.5

and it is not working
Attachment:
New Microsoft Word Document.doc [57 KiB]

Kudos [?]: 61 [0], given: 0

Manager
Joined: 02 Jan 2008
Posts: 157

Kudos [?]: 132 [0], given: 0

### Show Tags

09 Feb 2008, 14:56
are you solving for v?

btw, you will get v=33 (v^2 = 1089) and answer should be 2.5

Kudos [?]: 132 [0], given: 0

Senior Manager
Joined: 18 Jun 2007
Posts: 287

Kudos [?]: 61 [0], given: 0

### Show Tags

10 Feb 2008, 10:54
yup, I was trying to get the answer through v..I was pretty late last night..got it right in the morning. thx

Kudos [?]: 61 [0], given: 0

CEO
Joined: 29 Mar 2007
Posts: 2554

Kudos [?]: 511 [0], given: 0

### Show Tags

10 Feb 2008, 21:52
rishi2377 wrote:
I got this correct through backsolving....but didn't get it through direct method...
Here is what i tried:

(90/v-3) - (90/v+3) = 0.5
= > {90*(v+3)} - {90*(v-3)}/ v^2 - 3^2 = 0.5

and it is not working
Attachment:
New Microsoft Word Document.doc

Man this was kindof a nasty lil problem. Easy conceptually, but lots of busy work.

(v-3)(t+1/2)=90
(v+3)(t)=90

vt+v/2-3t-3/2=90
vt+3t

2vt+v-6t=183
-2(vt+3)=90(-2) ---> v=12t+3

(12t+6)(t)=90 ----> t^2+(t/2)^2-15/2=0 ---> (t+3)(t-5/2)=0 so t=2.5

i think a better approach would be to just plug in the answer choices.

Kudos [?]: 511 [0], given: 0

Senior Manager
Joined: 18 Jun 2007
Posts: 287

Kudos [?]: 61 [0], given: 0

### Show Tags

12 Feb 2008, 07:06
GMATBLACKBELT wrote:
rishi2377 wrote:
I got this correct through backsolving....but didn't get it through direct method...
Here is what i tried:

(90/v-3) - (90/v+3) = 0.5
= > {90*(v+3)} - {90*(v-3)}/ v^2 - 3^2 = 0.5

and it is not working
Attachment:
New Microsoft Word Document.doc

Man this was kindof a nasty lil problem. Easy conceptually, but lots of busy work.

(v-3)(t+1/2)=90
(v+3)(t)=90

vt+v/2-3t-3/2=90
vt+3t

2vt+v-6t=183
-2(vt+3)=90(-2) ---> v=12t+3

(12t+6)(t)=90 ----> t^2+(t/2)^2-15/2=0 ---> (t+3)(t-5/2)=0 so t=2.5

i think a better approach would be to just plug in the answer choices.

lol yes black belt...I got it correct through backsolving but tried to get it through direct method and gu6ess what, it was 0315 in the morning. lol thx anyway.

Kudos [?]: 61 [0], given: 0

GMAT Instructor
Joined: 04 Jul 2006
Posts: 1259

Kudos [?]: 335 [0], given: 0

### Show Tags

12 Feb 2008, 07:13
rishi2377 wrote:
I got this correct through backsolving....but didn't get it through direct method...
Here is what i tried:

(90/v-3) - (90/v+3) = 0.5
= > {90*(v+3)} - {90*(v-3)}/ v^2 - 3^2 = 0.5

and it is not working
Attachment:
New Microsoft Word Document.doc

Looks good so far! Rather that factoring to get v^2=1089, we can do the following:
Multiply be 2 to get 180/(v-3) - 180/(v+3) = 1

Look for two factors of 180 = 2^2*3^2*5 that differ by 6: 30 and 36. Thus v=33

Kudos [?]: 335 [0], given: 0

Re: PS: Prep   [#permalink] 12 Feb 2008, 07:13
Display posts from previous: Sort by