Find all School-related info fast with the new School-Specific MBA Forum

It is currently 24 Oct 2014, 04:32

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

What is the value of t ?

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
SVP
SVP
User avatar
Joined: 06 Sep 2013
Posts: 1773
Location: United States
Concentration: Finance
GMAT 1: 710 Q48 V39
WE: Corporate Finance (Investment Banking)
Followers: 15

Kudos [?]: 198 [0], given: 307

GMAT ToolKit User
What is the value of t ? [#permalink] New post 01 Oct 2013, 14:28
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

68% (01:47) correct 32% (00:49) wrong based on 50 sessions
What is the value of t ?

(1) The average (arithmetic mean) of t^2 and 8t is –8.
(2) \sqrt{t^4} = 16
[Reveal] Spoiler: OA

Last edited by Bunuel on 02 Oct 2013, 01:06, edited 1 time in total.
Edited the second statement.
Expert Post
Magoosh GMAT Instructor
User avatar
Joined: 28 Dec 2011
Posts: 2142
Followers: 539

Kudos [?]: 2278 [0], given: 31

Re: What is the value of t ? [#permalink] New post 01 Oct 2013, 15:28
Expert's post
jlgdr wrote:
What is the value of t ?

(1) The average (arithmetic mean) of t^2 and 8t is –8.
(2) t^1/4 = 16

I'm happy to help :-), but I disagree with the OA given.

Statement #1: The average (arithmetic mean) of t^2 and 8t is –8.
[t^2 + 8t]/2 = –8
t^2 + 8t = –16
t^2 + 8t + 16 = 0
(t + 4)^2 = 0
t = - 4
See:
http://magoosh.com/gmat/2013/three-alge ... -the-gmat/
This statement produces a unique value of t, and thus is sufficient.

Statement #2: t^1/4 = 16
I will assume what this means is t^(1/4) = 16, only because I can't think of another sensible interpretation of the ambiguity. Incidentally, on the issue of this ambiguity, and the underlying mathematical principles, read:
http://magoosh.com/gmat/2013/gmat-quant ... g-symbols/
Raising a number to the power of (1/4) is equivalent to taking the fourth root of a number. We can't take an even root of negative number, so if the fourth root of t equals anything sensible, then t absolutely must be positive. We would raise both sides to the fourth power to get a unique value of t. See:
http://magoosh.com/gmat/2012/exponent-p ... -the-gmat/
(BTW, that value would be t = 2^16 = 65,536, but absolutely no one expects you to get that without a calculator!!)
This statement also produces a unique value of t, and thus is also sufficient.

This would produce an OA of (D). I don't know whether you copied something incorrectly about statement two --- perhaps another phrasing would make that statement insufficient. Also, as this question currently stands, the two statements produce different values for t. This falls short of the standard that the GMAT keeps on DS --- statements in both statements are mathematically consistent.

Let me know if statement #2 says something else.

Mike :-)
_________________

Mike McGarry
Magoosh Test Prep

Image

Image


Last edited by mikemcgarry on 02 Oct 2013, 09:03, edited 2 times in total.
Expert Post
Magoosh GMAT Instructor
User avatar
Joined: 28 Dec 2011
Posts: 2142
Followers: 539

Kudos [?]: 2278 [0], given: 31

Re: What is the value of t ? [#permalink] New post 01 Oct 2013, 15:33
Expert's post
jlgdr wrote:
What is the value of t ?
(1) The average (arithmetic mean) of t^2 and 8t is –8.
(2) t^1/4 = 16

I just did a web search, and found this version of statement #2:

Statement #2: sqrt(t^4) = 16

Unlike the version you quoted, this version would indeed be insufficient, because it would allow for both t = +4 and t = -4. Furthermore, the correct answer from statement #1 is one of the possible answers in statement #2, so indeed, the statements here are mathematically consistent with one another.

Was this your question?
Mike :-)
_________________

Mike McGarry
Magoosh Test Prep

Image

Image

Manager
Manager
avatar
Joined: 10 Sep 2013
Posts: 80
Concentration: Sustainability, International Business
Followers: 0

Kudos [?]: 34 [0], given: 2

Re: What is the value of t ? [#permalink] New post 01 Oct 2013, 15:55
mikemcgarry wrote:
jlgdr wrote:
What is the value of t ?

(1) The average (arithmetic mean) of t^2 and 8t is –8.
(2) t^1/4 = 16

I'm happy to help :-), but I disagree with the OA given.

Statement #1: The average (arithmetic mean) of t^2 and 8t is –8.
[t^2 + 8t]/2 = –8
t^2 + 8t = –16
t^2 + 8t + 16 = 0
(t - 4)^2 = 0
t = 4
See:
http://magoosh.com/gmat/2013/three-alge ... -the-gmat/
This statement produces a unique value of t, and thus is sufficient.

Statement #2: t^1/4 = 16
I will assume what this means is t^(1/4) = 16, only because I can't think of another sensible interpretation of the ambiguity. Incidentally, on the issue of this ambiguity, and the underlying mathematical principles, read:
http://magoosh.com/gmat/2013/gmat-quant ... g-symbols/
Raising a number to the power of (1/4) is equivalent to taking the fourth root of a number. We can't take an even root of negative number, so if the fourth root of t equals anything sensible, then t absolutely must be positive. We would raise both sides to the fourth power to get a unique value of t. See:
http://magoosh.com/gmat/2012/exponent-p ... -the-gmat/
(BTW, that value would be t = 2^16 = 65,536, but absolutely no one expects you to get that without a calculator!!)
This statement also produces a unique value of t, and thus is also sufficient.

This would produce an OA of (D). I don't know whether you copied something incorrectly about statement two --- perhaps another phrasing would make that statement insufficient. Also, as this question currently stands, the two statements produce different values for t. This falls short of the standard that the GMAT keeps on DS --- statements in both statements are mathematically consistent.

Let me know if statement #2 says something else.

Mike :-)


t^2 + 8t + 16 = 0
Shouldn't this be: (t + 4)^2 = 0 ?
_________________

Kudos if I helped :)

Expert Post
Magoosh GMAT Instructor
User avatar
Joined: 28 Dec 2011
Posts: 2142
Followers: 539

Kudos [?]: 2278 [0], given: 31

Re: What is the value of t ? [#permalink] New post 01 Oct 2013, 16:04
Expert's post
igotthis wrote:
t^2 + 8t + 16 = 0
Shouldn't this be: (t + 4)^2 = 0 ?

YES! Absolutely! I just corrected it in my post above.
Thanks,
Mike :-)
_________________

Mike McGarry
Magoosh Test Prep

Image

Image

Manager
Manager
avatar
Joined: 10 Sep 2013
Posts: 80
Concentration: Sustainability, International Business
Followers: 0

Kudos [?]: 34 [0], given: 2

Re: What is the value of t ? [#permalink] New post 01 Oct 2013, 17:13
mikemcgarry wrote:
igotthis wrote:
t^2 + 8t + 16 = 0
Shouldn't this be: (t + 4)^2 = 0 ?

YES! Absolutely! I just corrected it in my post above.
Thanks,
Mike :-)


Sorry, I know this statement is suff. since it gives a unique value...but shouldn't t = -4 then?
_________________

Kudos if I helped :)

Expert Post
1 KUDOS received
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 23408
Followers: 3611

Kudos [?]: 28882 [1] , given: 2859

Re: What is the value of t ? [#permalink] New post 02 Oct 2013, 01:09
1
This post received
KUDOS
Expert's post
jlgdr wrote:
What is the value of t ?

(1) The average (arithmetic mean) of t^2 and 8t is –8.
(2) \sqrt{t^4} = 16


NOTE: edited the second statement.

What is the value of t ?

(1) The average (arithmetic mean) of t^2 and 8t is –8 --> t^2 + 8t = -8*2 --> t^2 + 8t + 16 = 0 --> (t+4)^2 = 0 --> t = -4. Sufficient.

(2) \sqrt{t^4} = 16 --> t^2 = 16 --> t = -4 or t = 4. Not sufficient.

Answer: A.

Hope it helps.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
25 extra-hard Quant Tests

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Expert Post
Magoosh GMAT Instructor
User avatar
Joined: 28 Dec 2011
Posts: 2142
Followers: 539

Kudos [?]: 2278 [0], given: 31

Re: What is the value of t ? [#permalink] New post 02 Oct 2013, 09:04
Expert's post
igotthis wrote:
Sorry, I know this statement is suff. since it gives a unique value...but shouldn't t = -4 then?

Yes, just changed it.
Mike :-)
_________________

Mike McGarry
Magoosh Test Prep

Image

Image

Re: What is the value of t ?   [#permalink] 02 Oct 2013, 09:04
    Similar topics Author Replies Last post
Similar
Topics:
Experts publish their posts in the topic What is the value of a ? atalpanditgmat 6 03 Apr 2013, 08:21
Experts publish their posts in the topic what is the value? smitakokne 1 19 Dec 2010, 07:17
What is the value of │x + 7│? M8 7 05 May 2006, 19:46
DS - What is the value of b? sundarman 5 18 Sep 2005, 07:23
Display posts from previous: Sort by

What is the value of t ?

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| 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®.