GMAT Question of the Day: Daily via email | Daily via Instagram New to GMAT Club? Watch this Video

It is currently 03 Aug 2020, 04:50

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

Three congruent circles overlap in such a way that each circ

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

Hide Tags

Find Similar Topics 
Manager
Manager
avatar
Joined: 09 Feb 2013
Posts: 107
Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post Updated on: 15 Sep 2017, 04:43
5
27
00:00
A
B
C
D
E

Difficulty:

  95% (hard)

Question Stats:

54% (02:51) correct 46% (02:37) wrong based on 249 sessions

HideShow timer Statistics

Image
Three congruent circles overlap in such a way that each circle intersects the centers of both of the other circles, as shown below. If the radius of each of the circles is 8, what is the area of the central section where all three circles overlap?

A. \(16\sqrt{3}\)

B. \(32(\pi-\sqrt{3})\)

C. \(16(\pi+\sqrt{3})\)

D. \(32\pi\)

E. \(32(\pi+\sqrt{3})\)

Attachment:
2.jpg
2.jpg [ 8.43 KiB | Viewed 23971 times ]

Originally posted by emmak on 11 Mar 2013, 23:48.
Last edited by Bunuel on 15 Sep 2017, 04:43, edited 2 times in total.
Edited the question.
Most Helpful Expert Reply
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 65761
Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post 12 Mar 2013, 02:10
5
8
emmak wrote:
Image
Three congruent circles overlap in such a way that each circle intersects the centers of both of the other circles, as shown below. If the radius of each of the circles is 8, what is the area of the central section where all three circles overlap?

A. \(16\sqrt{3}\)

B. \(32(\pi-\sqrt{3})\)

C. \(16(\pi+\sqrt{3})\)

D. \(32\pi\)

E. \(32(\pi+\sqrt{3})\)


I'd go with approximation with this question. Look at the diagram below:

Image

Notice that triangle ABC is equilateral (all sides are radii of the circles, for example AB and AC are radii of the lower circle and BC is radius of both upper circles). This implies that angle A is 60 degrees, thus the area of sector ABC (yellow region in the lower circle) is 1/6th of the area of the circle, so it's area is \(\frac{8^2\pi}{6}\approx{34}\).

Now, the area of the region we need to find must be more than this but not too much. Only B fits.

Answer: B.

Hope it's clear.

Attachment:
Circles.png
Circles.png [ 21.94 KiB | Viewed 23818 times ]

_________________
General Discussion
Intern
Intern
avatar
Joined: 20 Jan 2013
Posts: 2
Re: Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post 13 Mar 2013, 19:19
The area of the overlapping section should be little less than the half of the area of the circle , and only B fits
Veritas Prep GMAT Instructor
User avatar
V
Joined: 16 Oct 2010
Posts: 10780
Location: Pune, India
Re: Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post 13 Mar 2013, 19:43
9
3
emmak wrote:
Attachment:
2.jpg
Three congruent circles overlap in such a way that each circle intersects the centers of both of the other circles, as shown below. If the radius of each of the circles is 8, what is the area of the central section where all three circles overlap?

A. \(16\sqrt{3}\)

B. \(32(\pi-\sqrt{3})\)

C. \(16(\pi+\sqrt{3})\)

D. \(32\pi\)

E. \(32(\pi+\sqrt{3})\)


To get the exact answer, we can just follow Bunuel's solution a little further.

Area of overlap = Area of sector ABC + 2 (Area of sector ABC - Area of triangle ABC) (or you can also look at it as Area of overlap = 3*Area of sector ABC - 2*Area of triangle ABC)

Area of overlap \(= \frac{64\pi}{6} + 2(\frac{64\pi}{6} - \frac{\sqrt{3}*64}{4})\)
Area of overlap = \(32(\pi - \sqrt{3})\)
_________________
Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >
Intern
Intern
avatar
Joined: 07 Dec 2012
Posts: 9
Reviews Badge
Re: Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post 26 Sep 2016, 05:42
Hello Bunuel / Krishna, please critique my logic below:

Let us consider top left circle as A, top right as B, and below circle as C.

As the radius is 8, each circle's area would be 64π ,
Total area of all 3 circles combined: 64π * 3 = 192π.

As the overlap is between two radiuses of the circles, we can consider that there is 1/2 of overlap between circles A, B and 1/4 overlap between A and C, similar would be the case for all 3 circles. Therefore in total, for each circle, the overlap of the area is 3/4*(64π) = 16π.

So basically, each section above is 16π including the central area.

The only answer closer to 16π is 32(π−3‾√) .

So the answer is B.
Manager
Manager
avatar
S
Joined: 03 Jun 2015
Posts: 76
Re: Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post 07 Jul 2017, 06:49
VeritasPrepKarishma wrote:
emmak wrote:
Attachment:
2.jpg
Three congruent circles overlap in such a way that each circle intersects the centers of both of the other circles, as shown below. If the radius of each of the circles is 8, what is the area of the central section where all three circles overlap?

A. \(16\sqrt{3}\)

B. \(32(\pi-\sqrt{3})\)

C. \(16(\pi+\sqrt{3})\)

D. \(32\pi\)

E. \(32(\pi+\sqrt{3})\)


To get the exact answer, we can just follow Bunuel's solution a little further.

Area of overlap = Area of sector ABC + 2 (Area of sector ABC - Area of triangle ABC) (or you can also look at it as Area of overlap = 3*Area of sector ABC - 2*Area of triangle ABC)

Area of overlap \(= \frac{64\pi}{6} + 2(\frac{64\pi}{6} - \frac{\sqrt{3}*64}{4})\)
Area of overlap = \(32(\pi - \sqrt{3})\)


Hi VeritasPrepKarishma

Could you please elaborate on the green highlight. I understand that the area of the over lap in 3 * sector area which is \(32\pi\), however, I was lost with 2* area of triangle. Could you please explain?

Thanks in advance.
_________________
Sortem sternit fortem!
Veritas Prep GMAT Instructor
User avatar
V
Joined: 16 Oct 2010
Posts: 10780
Location: Pune, India
Re: Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post 15 Sep 2017, 01:28
emmak wrote:
Attachment:
2.jpg
Three congruent circles overlap in such a way that each circle intersects the centers of both of the other circles, as shown below. If the radius of each of the circles is 8, what is the area of the central section where all three circles overlap?

A. \(16\sqrt{3}\)

B. \(32(\pi-\sqrt{3})\)

C. \(16(\pi+\sqrt{3})\)

D. \(32\pi\)

E. \(32(\pi+\sqrt{3})\)


Responding to a pm:
Quote:
A query regarding this question:

Can you explain the region of overlap again?

I thought it was 3 * each small sectors formed by 60deg central angle + area of eq. triangle


Yes, you are right. You mean that the area is the area of triangle + 3* area of the small segment

Here is the problem with that approach - we don't know the area of the small segment. So it involves an additional step of first finding the area of the sector and then subtracting the area of the triangle out of it. Let me explain.

If we consider the area of the sector and try to find the answer in those terms, it will be easier. The sector is made by the sides AB, AC and the arc BC. We know that if we know the central angle, finding the area of such a sector is easy provided we know the radius of the circle.

Area of the sector = (Q/360) * pi*r^2

Of course, if we know the area of the sector, we can subtract the area of the triangle from it and that will give us the area of the segment (between arc BC and side BC). Thereafter, you can use your own approach.
_________________
Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >
Intern
Intern
avatar
B
Joined: 24 Jul 2017
Posts: 43
Location: India
WE: Information Technology (Computer Software)
Re: Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post 15 Sep 2017, 04:35
This is how I approached the problem :

Since radii of all the circles are equal, an equilateral triangle will be formed inside the common region.
To find the area of common region, we can simply follow
A(common region) = 3* Area of sector inside the common region - 3* Area of equilateral triangle
= 3* (60/360) * pi * 8^2 - 3 * (sqrt3 * 8^2/4)
Further simplifying, we get option B as answer

Hope it helps :)
Senior Manager
Senior Manager
avatar
P
Joined: 27 Dec 2016
Posts: 300
Re: Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post 01 Dec 2018, 19:05
Bunuel wrote:
emmak wrote:
Image
Three congruent circles overlap in such a way that each circle intersects the centers of both of the other circles, as shown below. If the radius of each of the circles is 8, what is the area of the central section where all three circles overlap?

A. \(16\sqrt{3}\)

B. \(32(\pi-\sqrt{3})\)

C. \(16(\pi+\sqrt{3})\)

D. \(32\pi\)

E. \(32(\pi+\sqrt{3})\)


I'd go with approximation with this question. Look at the diagram below:

Image

Notice that triangle ABC is equilateral (all sides are radii of the circles, for example AB and AC are radii of the lower circle and BC is radius of both upper circles). This implies that angle A is 60 degrees, thus the area of sector ABC (yellow region in the lower circle) is 1/6th of the area of the circle, so it's area is \(\frac{8^2\pi}{6}\approx{34}\).

Now, the area of the region we need to find must be more than this but not too much. Only B fits.

Answer: B.

Hope it's clear.

Attachment:
Circles.png


Hi Bunuel,

I was wondering could you please explain how you deduced the middle part to be "1/6th of the area of the circle"?

Thank You!
GMATH Teacher
User avatar
P
Status: GMATH founder
Joined: 12 Oct 2010
Posts: 938
Re: Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post 16 Dec 2018, 05:28
2
1
emmak wrote:
Image
Three congruent circles overlap in such a way that each circle intersects the centers of both of the other circles, as shown below. If the radius of each of the circles is 8, what is the area of the central section where all three circles overlap?

A. \(16\sqrt{3}\)

B. \(32(\pi-\sqrt{3})\)

C. \(16(\pi+\sqrt{3})\)

D. \(32\pi\)

E. \(32(\pi+\sqrt{3})\)

My solution (presented below) follows Bunuel´s idea and one of VeritasKarishma´s comments.

I have decided to post it so that readers may study it explicitly:


Image


\(? = {S_{\Delta {\rm{equil}}}} + \,\,3 \cdot \,{S_{{\rm{blue}}}}\)

\({S_{\Delta {\rm{equil}}}} = {{{r^{\,2}}\sqrt 3 } \over 4}\,\,\,\mathop = \limits^{r\, = \,8} \,\,16\sqrt 3\)

\({S_{{\rm{blue}}}} = {{60} \over {360}}\left( {\pi \cdot {8^2}} \right) - {S_{\Delta {\rm{equil}}}} = {{\pi \cdot {8^2}} \over 6} - \,16\sqrt 3 = 8\left( {{{4\pi } \over 3} - 2\sqrt 3 } \right)\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,\,\,3 \cdot \,{S_{{\rm{blue}}}} = 8\left( {4\pi - 6\sqrt 3 } \right)\)


\(? = \,\,16\sqrt 3 + 8\left( {4\pi - 6\sqrt 3 } \right) = 32\left( {\pi - \sqrt 3 } \right)\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,\,\left( {\rm{B}} \right)\)


Regards,
Fabio.
_________________
Fabio Skilnik :: GMATH method creator (Math for the GMAT)
Our high-level "quant" preparation starts here: https://gmath.net
Intern
Intern
avatar
B
Joined: 02 Jul 2018
Posts: 23
Re: Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post 30 May 2019, 07:19

OFFICIAL SOLUTION



Answer: (B) This is a great example of when filling in the info you know and adding to the figure given helps point you in the right direction for solving what may initially be a confusing, complex question. You’re told the radius of each circle is 8, and that each circle intersects the centers of both the other circles. Therefore, if you connected the centers, the length of each line segment would be the radius and would create an equilateral triangle with side length 8 within the central segment:



From here you can portion that central area into smaller segments: the equilateral triangle, and three congruent arced segments on each of the three sides (see below for illustration of one of the segments):


Therefore, the area of the central region will be equal to the area of the triangle plus three times the area of that small arced segment. First go ahead and calculate the area of the equilateral triangle using the formula for that area:
s^2root3/4 you know that the area of the triangle is 16root 3.

Next calculate the area of one of the small segments. For the segments, you need to calculate the area of a sector - area of the equilateral triangle. Since each sector is 60° out of the full 360° in a triangle (since they form an equilateral triangle, which must have all angles measuring 60°), the area is 1/6. f the full area of the circle; the radius is 8, so the area of the circle is 64π, so the area of the sector is 32π/3. To find the segment you need to subtract the equilateral triangle from the sector which is: 32π/3−16root3. Since there are three segments, the area of those will be multiplied by 3. Lastly add that to the equilateral triangle.Thus the answer is B
Attachments

File comment: Image 2
Geometry_Q13SolutionImage2.jpg
Geometry_Q13SolutionImage2.jpg [ 2.83 KiB | Viewed 2958 times ]

File comment: Image 1
Geometry_Q13SolutionImage1.jpg
Geometry_Q13SolutionImage1.jpg [ 5.46 KiB | Viewed 2953 times ]

Intern
Intern
avatar
B
Joined: 15 Jul 2019
Posts: 24
Location: United Kingdom
GMAT 1: 730 Q49 V40
Reviews Badge
Three congruent circles overlap in such a way that each circ  [#permalink]

Show Tags

New post 11 Dec 2019, 11:34
VeritasKarishma wrote:
emmak wrote:
Attachment:
2.jpg
Three congruent circles overlap in such a way that each circle intersects the centers of both of the other circles, as shown below. If the radius of each of the circles is 8, what is the area of the central section where all three circles overlap?

A. \(16\sqrt{3}\)

B. \(32(\pi-\sqrt{3})\)

C. \(16(\pi+\sqrt{3})\)

D. \(32\pi\)

E. \(32(\pi+\sqrt{3})\)


To get the exact answer, we can just follow Bunuel's solution a little further.

Area of overlap = Area of sector ABC + 2 (Area of sector ABC - Area of triangle ABC) (or you can also look at it as Area of overlap = 3*Area of sector ABC - 2*Area of triangle ABC)

Area of overlap \(= \frac{64\pi}{6} + 2(\frac{64\pi}{6} - \frac{\sqrt{3}*64}{4})\)
Area of overlap = \(32(\pi - \sqrt{3})\)


\(32(\pi - \sqrt{3})\)
\(96(\pi - \sqrt{3})\)
GMAT Club Bot
Three congruent circles overlap in such a way that each circ   [#permalink] 11 Dec 2019, 11:34

Three congruent circles overlap in such a way that each circ

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





cron

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