GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 18 Apr 2019, 09:50

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

What is the value of y^3 - t^3?

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

Hide Tags

 
Retired Moderator
User avatar
Status: 2000 posts! I don't know whether I should feel great or sad about it! LOL
Joined: 04 Oct 2009
Posts: 1100
Location: Peru
Schools: Harvard, Stanford, Wharton, MIT & HKS (Government)
WE 1: Economic research
WE 2: Banking
WE 3: Government: Foreign Trade and SMEs
What is the value of y^3 - t^3?  [#permalink]

Show Tags

New post 23 Nov 2011, 09:57
1
5
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

69% (01:35) correct 31% (01:37) wrong based on 284 sessions

HideShow timer Statistics

What is the value of y^3 - t^3?

(1) y - t = 3
(2) y^2 - t^2 = 21

Source: gmathacks.com

_________________
"Life’s battle doesn’t always go to stronger or faster men; but sooner or later the man who wins is the one who thinks he can."

My Integrated Reasoning Logbook / Diary: http://gmatclub.com/forum/my-ir-logbook-diary-133264.html

GMAT Club Premium Membership - big benefits and savings
Manager
Manager
avatar
Joined: 13 May 2011
Posts: 222
WE 1: IT 1 Yr
WE 2: Supply Chain 5 Yrs
Re: What is the value of y^3 - t^3?  [#permalink]

Show Tags

New post 23 Nov 2011, 11:31
1. + 2.
(y+t)(y-t)=21
3*(y+t)=21
Y+t=7 and y-t=3 so we can solve for both t and y.
Senior Manager
Senior Manager
avatar
B
Joined: 24 Aug 2009
Posts: 462
Schools: Harvard, Columbia, Stern, Booth, LSB,
Re: What is the value of y^3 - t^3?  [#permalink]

Show Tags

New post 13 Sep 2012, 12:55
2
metallicafan wrote:
A fast way to solve this question? I solved it, but it took me more than 2 min :s.

What is the value of \(y^3 - t^3\)?
(1) \(y - t = 3\)
(2) \(y^2 - t^2 = 21\)

I spent a lot of time in solving the equations with the possible values of y and t.

Source: gmathacks.com



(1) - (y-t) = 3 ----> Y & t can be anything -Insufficient
(2) (y+t)(y-t) = 3 x 7 ----> (y+t) can be 3 or 7 -----> i.e. y will be 5 for sure but t can be 2 or -2 ----> Insufficient
(1+2) (y+t)= 7 because (y-t) = 3----> y = 5 & t=2--->Sufficient

Hope it helps.
_________________
If you like my Question/Explanation or the contribution, Kindly appreciate by pressing KUDOS.
Kudos always maximizes GMATCLUB worth
-Game Theory

If you have any question regarding my post, kindly pm me or else I won't be able to reply
Board of Directors
User avatar
P
Joined: 01 Sep 2010
Posts: 3354
Re: What is the value of y^3 - t^3?  [#permalink]

Show Tags

New post 13 Sep 2012, 13:39
y^3 - t^3 or x^3 - y^3 is the same if you are more comfortable

(x-y) * (x^2 - y^2) -----> (x - y) * (x - y) * (x + y)

1) x - y = 3 -----> 3 * 3 * (x + y) ----> we do no have the value od (x + Y)

2) we have 21 BUT not (x - y)

1) + 2) we have 3 * 21 ----> Sufficient

;)
_________________
Senior Manager
Senior Manager
avatar
B
Joined: 24 Aug 2009
Posts: 462
Schools: Harvard, Columbia, Stern, Booth, LSB,
Re: What is the value of y^3 - t^3?  [#permalink]

Show Tags

New post 13 Sep 2012, 14:14
1
carcass wrote:
y^3 - t^3 or x^3 - y^3 is the same if you are more comfortable

(x-y) * (x^2 - y^2) -----> (x - y) * (x - y) * (x + y)

1) x - y = 3 -----> 3 * 3 * (x + y) ----> we do no have the value od (x + Y)

2) we have 21 BUT not (x - y)

1) + 2) we have 3 * 21 ----> Sufficient

;)


Hi Carcass,

You are right that it does not make any difference between y,t & x,y.

But you made a mistake in the formula \(x^3-y^3\) is not equal to \((x-y)\) * \((x^2 - y^2)\)
Instead \((x-y)^3\) is equal to \(x^3-y^3\) + \(3xy(x-y)\)

I Hope it helps.
_________________
If you like my Question/Explanation or the contribution, Kindly appreciate by pressing KUDOS.
Kudos always maximizes GMATCLUB worth
-Game Theory

If you have any question regarding my post, kindly pm me or else I won't be able to reply
Board of Directors
User avatar
P
Joined: 01 Sep 2010
Posts: 3354
Re: What is the value of y^3 - t^3?  [#permalink]

Show Tags

New post 13 Sep 2012, 16:08
fameatop wrote:
carcass wrote:
y^3 - t^3 or x^3 - y^3 is the same if you are more comfortable

(x-y) * (x^2 - y^2) -----> (x - y) * (x - y) * (x + y)

1) x - y = 3 -----> 3 * 3 * (x + y) ----> we do no have the value od (x + Y)

2) we have 21 BUT not (x - y)

1) + 2) we have 3 * 21 ----> Sufficient

;)


Hi Carcass,

You are right that it does not make any difference between y,t & x,y.

But you made a mistake in the formula \(x^3-y^3\) is not equal to \((x-y)\) * \((x^2 - y^2)\)
Instead \((x-y)^3\) is equal to \(x^3-y^3\) + \(3xy(x-y)\)

I Hope it helps.
:shocked :wall ...........oh lord, after a long day of work the gmat is even worse.

Some Mod could say how to attack this question properly AND in the faster manner
_________________
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 54369
Re: What is the value of y^3 - t^3?  [#permalink]

Show Tags

New post 14 Sep 2012, 04:41
1
1
What is the value of y^3 - t^3?

(1) y - t = 3. If \(y=3\) and \(t=0\), we have one value for \(y^3 - t^3\) and for \(y=4\) and \(t=1\) another. Not sufficient.

(2) y^2 - t^2 = 21. The same here. Not sufficient.

(1)+(2) From (2) we have \((y-t)(y+t)=21\). Since from (1) \(y - t = 3\), then \(3(y+t)=21\) --> \(y+t=7\). So we have two distinct linear equation with two unknowns: \(y+t=7\) and \(y - t = 3\), which means that we can solve for them and get the value of \(y^3 - t^3\). Sufficient.

Answer: C.

Hope it's clear.
_________________
Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 10543
Re: What is the value of y^3 - t^3?  [#permalink]

Show Tags

New post 17 Aug 2017, 19:22
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.
_________________
GMAT Club Bot
Re: What is the value of y^3 - t^3?   [#permalink] 17 Aug 2017, 19:22
Display posts from previous: Sort by

What is the value of y^3 - t^3?

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

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

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.