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

It is currently 25 Jul 2014, 03:20

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 will be the percentage increase in the area of the cube

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Manager
Manager
avatar
Joined: 23 Oct 2011
Posts: 54
Location: Ukraine
Schools: LBS '14 (M)
GMAT 1: 650 Q44 V35
WE: Corporate Finance (Mutual Funds and Brokerage)
Followers: 2

Kudos [?]: 20 [0], given: 7

What will be the percentage increase in the area of the cube [#permalink] New post 21 Apr 2012, 01:07
00:00
A
B
C
D
E

Difficulty:

  25% (low)

Question Stats:

66% (01:43) correct 34% (00:44) wrong based on 115 sessions
What will be the percentage increase in the area of the cube's surface if each of the cube's edges grows by 20%?

A. 33%
B. 44%
C. 55%
D. 56%
E. 73%
[Reveal] Spoiler: OA

Last edited by JubtaGubar on 23 Apr 2012, 07:18, edited 1 time in total.
Manager
Manager
avatar
Joined: 23 Oct 2011
Posts: 54
Location: Ukraine
Schools: LBS '14 (M)
GMAT 1: 650 Q44 V35
WE: Corporate Finance (Mutual Funds and Brokerage)
Followers: 2

Kudos [?]: 20 [0], given: 7

Re: Geometry: What will be the percentage increase in the area [#permalink] New post 21 Apr 2012, 01:12
JubtaGubar wrote:
What will be the percentage increase in the area of the cube's surface if each of the cube's edges grows by 20%?
(A) 33%
(B) 44%
(C) 55%
(D) 56%
(E) 73%


The question is very easy. My logic is the following:
A surface = 6*a^2
After 20% increase A surface = 6* ((1.2a)^2) = 6*1.44*a^2
The increase in the surface area = (6*1.44*a^2 - 6*a^2)/6*a^2 = (6*a^2(1.44-1))/(6*a^2) = 1.44-1=0.44 = 44%

but the official answer is different...

Could you please advise what is wrong with my solution or the official answer is not correct?
Expert Post
2 KUDOS received
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 18737
Followers: 3243

Kudos [?]: 22383 [2] , given: 2616

Re: Geometry: What will be the percentage increase in the area [#permalink] New post 21 Apr 2012, 01:36
2
This post received
KUDOS
Expert's post
JubtaGubar wrote:
JubtaGubar wrote:
What will be the percentage increase in the area of the cube's surface if each of the cube's edges grows by 20%?
(A) 33%
(B) 44%
(C) 55%
(D) 56%
(E) 73%


The question is very easy. My logic is the following:
A surface = 6*a^2
After 20% increase A surface = 6* ((1.2a)^2) = 6*1.44*a^2
The increase in the surface area = (6*1.44*a^2 - 6*a^2)/6*a^2 = (6*a^2(1.44-1))/(6*a^2) = 1.44-1=0.44 = 44%

but the official answer is different...

Could you please advise what is wrong with my solution or the official answer is not correct?


Your solution is correct.

Say the edge of the cube is 10, its surface area is 6*100;
After 20% increase the edge becomes 12, so the new surface area is 6*144;

Percent increase=change/original=(6*144-6*100)/(6*100)*100=44%.

Or directly: the new surface area is 6*144=(6*100)*1.44 --> increase 44%.

Answer: B.
_________________

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

Intern
Intern
avatar
Joined: 19 Apr 2012
Posts: 3
Followers: 0

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

Re: What will be the percentage increase in the area of the cube [#permalink] New post 21 Apr 2012, 02:56
If you increase a line with %20 it the line will be 1,2/1
If we increase edges with %20 in a surface the area will be 1.2*1.2 =1.44
If we increase edges with %20 in a cube or 3D , the volume is 1.2*1.2 = 1.2*1.2*1.2

Your solution is correct but in order to minimize time to solve

It doesn't matter how many surface have a 3D object or how many edges have a 2D object
So you dont have to think about how many surface does it have.

The ratio of line increase with (100+A)^1
The ratio of area will be (100+A)^2
The ratio of volume will be (100+A)^3



In line the increase or decrease will be also linear. (100+A/100)
In 2D it will be (100+A/100)*(100+A/100) \\ second power
In 3D it will be (100+A/100)*(100+A/100)*(100+A/100) \\third power


All you need to do is just multiply 1.2 * 1.2 = 1.44 and so it is %44
That's all
Manager
Manager
avatar
Status: I will not stop until i realise my goal which is my dream too
Joined: 25 Feb 2010
Posts: 235
Schools: Johnson '15
Followers: 2

Kudos [?]: 20 [0], given: 16

GMAT Tests User
Re: What will be the percentage increase in the area of the cube [#permalink] New post 21 Apr 2012, 05:45
JubtaGubar wrote:
What will be the percentage increase in the area of the cube's surface if each of the cube's edges grows by 20%?

A. 33%
B. 44%
C. 55%
D. 56%
E. 73%



just like others, even i got 44% increase...but dont know OA says answer is D.....
_________________

Regards,
Harsha

Note: Give me kudos if my approach is right , else help me understand where i am missing.. I want to bell the GMAT Cat ;)

Satyameva Jayate - Truth alone triumphs

Manager
Manager
avatar
Joined: 23 Oct 2011
Posts: 54
Location: Ukraine
Schools: LBS '14 (M)
GMAT 1: 650 Q44 V35
WE: Corporate Finance (Mutual Funds and Brokerage)
Followers: 2

Kudos [?]: 20 [0], given: 7

Re: What will be the percentage increase in the area of the cube [#permalink] New post 23 Apr 2012, 07:19
Now I am sure that it is a mistake in the OA. I changed it to B.

Thank you all for confirming my solution!
Director
Director
User avatar
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 655
Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)
Followers: 3

Kudos [?]: 147 [0], given: 162

Re: What will be the percentage increase in the area of the cube [#permalink] New post 28 Feb 2013, 23:35
I did wrong. I used the volume formula & got wrong answer.
_________________

Kindly press "Kudos" to appreciate

Re: What will be the percentage increase in the area of the cube   [#permalink] 28 Feb 2013, 23:35
    Similar topics Author Replies Last post
Similar
Topics:
What is the surface area of the cube ? UtterNonsense 4 26 Jul 2011, 05:42
What is the ratio of the surface area of a cube to the pm4553 1 04 Oct 2008, 06:09
The shaded area is what percentage of the area of the jallenmorris 27 03 Jul 2008, 18:23
What will be the percentage increase in the area of a circle bmwhype2 3 16 Oct 2007, 11:52
What is the ratio of the surface area of a cube to the trahul4 6 12 Aug 2007, 04:18
Display posts from previous: Sort by

What will be the percentage increase in the area of the cube

  Question banks Downloads My Bookmarks Reviews Important topics  


cron

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®.