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TAGS: GRE Instructor Joined: 10 Apr 2015
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If each of the 4 circles above has radius 1, [#permalink]
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Expert's post 00:00

Question Stats: 85% (01:42) correct 14% (01:27) wrong based on 7 sessions If each of the 4 circles above has radius 1, what is the area of the shaded region?
A) 1 – π/4
B) 2 – π/4
C) 2 – π/2
D) 4 – π
E) 4 – 2π
[Reveal] Spoiler: OA

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Brent Hanneson – Creator of greenlighttestprep.com Sign up for our free GRE Question of the Day emails Director  Joined: 07 Jan 2018
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Re: If each of the 4 circles above has radius 1, [#permalink]
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In these four identical circles let us assume the center of the circle from left uppermost to left bottom most are a,b,c and d respectively

If we connect the center of the 4 circles we will get a square. Each side of the square will be of length 2

Now, the area of the square would be $$2 *2 = 4$$
We are required to find the area of the shaded region hence we should reduce the portion of the circle enclosed within the square that is not shaded.
Since the side of the square are at 90 degrees to each other we know that there are 4 right triangles within the square enclosed in the circle.

For this we should find the area of 4 sectors that are not shaded.
The area of each sector would be equal to the other three sector.

area of 1 sector = $$\frac{90}{360}$$ * ∏ * $$r^2 = \frac{1}{4} *$$ ∏ as radius = 1
for 4 sectors area would be $$\frac{1}{4} *$$ ∏ $$* 4$$ = ∏

Therefore, area of the shaded region = 4 - ∏
option D
Attachments circles.png [ 34.89 KiB | Viewed 495 times ]

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This is my response to the question and may be incorrect. Feel free to rectify any mistakes

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Re: If each of the 4 circles above has radius 1, [#permalink]
Expert's post
Outstanding explanation.

It should be put as sticky "answer of the month".

Regards
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GRE Instructor Joined: 10 Apr 2015
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Kudos [?]: 1481 , given: 8

Re: If each of the 4 circles above has radius 1, [#permalink]
Expert's post
GreenlightTestPrep wrote: If each of the 4 circles above has radius 1, what is the area of the shaded region?
A) 1 – π/4
B) 2 – π/4
C) 2 – π/2
D) 4 – π
E) 4 – 2π

Here's a different approach:

Let's place a square around just one of the circles Notice that the shaded area IN the square represents 1/4 of the TOTAL shaded area in the diagram. This means that the shaded area in THIS diagram will be the same as the TOTAL shaded area in the ORIGINAL diagram. So, let's determine the area of the shaded area in the diagram below. Each side of the square has length 2, so the area of the SQUARE = (2)(2) = 4

The circle has radius 1.
So, the area of the CIRCLE = π(radius)² = π(1)² = π

So, the area of the SHADED region = 4 - π

Cheers,
Brent
_________________

Brent Hanneson – Creator of greenlighttestprep.com Sign up for our free GRE Question of the Day emails Director  Joined: 07 Jan 2018
Posts: 604
Followers: 7

Kudos [?]: 546  , given: 88

Re: If each of the 4 circles above has radius 1, [#permalink]
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GreenlightTestPrep wrote:
GreenlightTestPrep wrote: If each of the 4 circles above has radius 1, what is the area of the shaded region?
A) 1 – π/4
B) 2 – π/4
C) 2 – π/2
D) 4 – π
E) 4 – 2π

Here's a different approach:

Let's place a square around just one of the circles Notice that the shaded area IN the square represents 1/4 of the TOTAL shaded area in the diagram. This means that the shaded area in THIS diagram will be the same as the TOTAL shaded area in the ORIGINAL diagram. So, let's determine the area of the shaded area in the diagram below. Each side of the square has length 2, so the area of the SQUARE = (2)(2) = 4

The circle has radius 1.
So, the area of the CIRCLE = π(radius)² = π(1)² = π

So, the area of the SHADED region = 4 - π

Cheers,
Brent

This approach would save some time

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This is my response to the question and may be incorrect. Feel free to rectify any mistakes Re: If each of the 4 circles above has radius 1,   [#permalink] 04 Jun 2018, 17:42
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