It is currently 20 Apr 2018, 21:03

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

The surface area of a sphere is 4πR2, where R is the radius of the sph

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

Hide Tags

Intern
Intern
avatar
Joined: 27 Jun 2014
Posts: 1
Concentration: Entrepreneurship, General Management
The surface area of a sphere is 4πR2, where R is the radius of the sph [#permalink]

Show Tags

New post 08 Feb 2015, 11:53
7
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

41% (00:52) correct 59% (00:54) wrong based on 153 sessions

HideShow timer Statistics

The surface area of a sphere is 4πR2, where R is the radius of the sphere. If the area of the base of a hemisphere is 3, what is the surface area of that hemisphere?
(A) 6/π
(B) 9/π
(C) 6
(D) 9
(E) 12
[Reveal] Spoiler: OA
1 KUDOS received
Manager
Manager
avatar
Joined: 23 Jan 2013
Posts: 165
Concentration: Technology, Other
Schools: Haas
GMAT Date: 01-14-2015
WE: Information Technology (Computer Software)
GMAT ToolKit User
Re: The surface area of a sphere is 4πR2, where R is the radius of the sph [#permalink]

Show Tags

New post 08 Feb 2015, 12:01
1
This post received
KUDOS
Given Area of the base of a hemisphere is 3 = PI * R^2
Thus R = Sqrt ( 3 / PI ) .

Surface area of whole sphere = 4*PI*R^2 .
= 4 * PI * 3 / PI
= 12 .
Since the hemisphere is half of a sphere the Surface area of the hemisphere = 12 / 2
= 6 ( curved part , not including the flat rounded base ) .

But the total surface area = 6 + Area of the base of a hemisphere .
= 6 + 3
= 9.
Answer is D !!
Intern
Intern
avatar
Joined: 10 Feb 2013
Posts: 14
Location: India
Concentration: General Management, Finance
GMAT Date: 05-16-2015
GPA: 3.67
WE: Programming (Computer Software)
Re: The surface area of a sphere is 4πR2, where R is the radius of the sph [#permalink]

Show Tags

New post 08 Feb 2015, 12:03
Stanislau wrote:
The surface area of a sphere is 4πR2, where R is the radius of the sphere. If the area of the base of a hemisphere is 3, what is the surface area of that hemisphere?
(A) 6/π
(B) 9/π
(C) 6
(D) 9
(E) 12


Surface area of the hemisphere is = (2πR2 + πR2 ( area of the base) ) =3πR2

Given

πR2 = 3

therefore surface area of the sphere = 3*3 = 9
Expert Post
2 KUDOS received
Veritas Prep GMAT Instructor
User avatar
Joined: 23 Oct 2013
Posts: 144
Re: The surface area of a sphere is 4πR2, where R is the radius of the sph [#permalink]

Show Tags

New post 17 May 2015, 18:11
2
This post received
KUDOS
Expert's post
This is an interesting question with a nice trap answer built in. The first step is to realize that the area of the base of the hemisphere can be represented by the area of a circle formula: A = pie*r^2. Because this equals 3, we know that pie*r^2 = 3. It is tempting at this point to then try to solve for r, but if you look at the area of the sphere formula you will see that it is better to leave it in pie*r^2 form. Always check before doing math to make sure that it is an efficient approach, and here solving for r will only waste time.

Because the area of a sphere is 4*pie*r^2, we know that the area of the outer portion of the hemisphere will be 2*pie*r^2, or 6. This 6 is the trap answer choice, because you cannot forget the base of the sphere (the 3) on the bottom. You can visualize this by thinking about an orange. The entire surface area of this orange is 12, but if you cut it in half and look at just a half of it, you have to take the bottom part (the center of the orange) into account, not just the peel around that half. Therefore 6+3 = 9, giving us answer choice D.

I hope this helps!
_________________

Brandon
Veritas Prep | GMAT Instructor

If you found this post helpful, please give me kudos!!! :)

Save $100 on Veritas Prep GMAT Courses And Admissions Consulting
Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.

Veritas Prep Reviews

Director
Director
User avatar
B
Joined: 04 Jun 2016
Posts: 617
GMAT 1: 750 Q49 V43
The surface area of a sphere is 4πR2, where R is the radius of the sph [#permalink]

Show Tags

New post 16 Jul 2016, 23:56
1
This post was
BOOKMARKED
StanS wrote:
The surface area of a sphere is 4πR2, where R is the radius of the sphere. If the area of the base of a hemisphere is 3, what is the surface area of that hemisphere?
(A) 6/π
(B) 9/π
(C) 6
(D) 9
(E) 12


It is slightly tricky question, if there is a concentration lapse on the part of the test taker.

Surface area of sphere = \(4πr^2\)
Therefore curved surface area of Half of the sphere (Hemisphere)=\(\frac{1}{2}*4πr^2 =2πr^2 .................[eq 1]\)

Now the area of the base of the hemisphere is 3
The base of the hemisphere is a circle
therefore
\(πr^2=3\)
\(r^2=\frac{3}{π}\)

Put this value of \(r^2=\frac{3}{π}\)in [eq 1] to find the surface of hemisphere
\(2π*\frac{3}{π} = 6\)

Here comes the tricky part. Now since the hemisphere has a curves surface area and ALSO A FLAT surface area at the base; the total surface area will be the sum of these two
Total surface area of the hemisphere will be 6+3=9
Answer is D
_________________

Posting an answer without an explanation is "GOD COMPLEX". The world doesn't need any more gods. Please explain you answers properly.
FINAL GOODBYE :- 17th SEPTEMBER 2016. .. 16 March 2017 - I am back but for all purposes please consider me semi-retired.

Senior Manager
Senior Manager
avatar
G
Joined: 02 Apr 2014
Posts: 469
The surface area of a sphere is 4πR2, where R is the radius of the sph [#permalink]

Show Tags

New post 20 Jan 2018, 09:38
classic GMAT trap to get into answer 6 ( i got trapped :))

Yes answer should be 9, we have to add base area 3 of the hemisphere to outer surface area of 6 to get 9
The surface area of a sphere is 4πR2, where R is the radius of the sph   [#permalink] 20 Jan 2018, 09:38
Display posts from previous: Sort by

The surface area of a sphere is 4πR2, where R is the radius of the sph

  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 | 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®.