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Intern  Joined: 08 May 2014
Posts: 7
The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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29 00:00

Difficulty:   55% (hard)

Question Stats: 64% (02:01) correct 36% (02:03) wrong based on 612 sessions

HideShow timer Statistics The center of a circle is (5, -2). (5, 7) is outside the circle, and (1, -2) is inside the circle. If the radius, r, is an integer, how many possible values are there for r?

(A) 4
(B) 5
(C) 6
(D) 7
(E) 8
Senior Manager  Joined: 13 Jun 2013
Posts: 271
Re: The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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5
5
anik89 wrote:
The center of a circle is (5, -2). (5, 7) is outside the circle, and (1, -2) is inside the circle. If the radius, r, is an
integer, how many possible values are there for r?
(A) 4
(B) 5
(C) 6
(D) 7
(E) 8

distance between the center of the circle (5,-2) and (1,-2) = $$\sqrt{(5-1)^2 + (-2+2)^2}$$ $$= 4$$

distance between the center of the circle (5,-2) and (5,7) = $$\sqrt{(5-5)^2 + (7+2)^2}$$ $$= 9$$

now, since point (1,-2) lies inside the circle, therefore radius of the circle will be greater than 4. and also since point (5,7) lies outside the circle, therefore radius of the circle will be less than 9

i.e. 4<r<9
now since r is an integer, therefore possible values of r are 5,6,7 and 8. hence answer should be A.
General Discussion
Director  G
Joined: 23 Jan 2013
Posts: 543
Schools: Cambridge'16
Re: The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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1
Idea is that possible radius is between two points: (1,-2) and (5,7)

5-1=4, meaning that point inside the circle is 4 numbers out of center (5,-2),
we should count it in Y axe in (5,7) direction, so -2+4=2 and radius is between 2 and 7.

7-2 =5 values of R, but 7 is out and maximal possible is 4

A
Intern  Joined: 27 Nov 2014
Posts: 44
Re: The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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1
The center of a circle is (5, -2). (5, 7) is outside the circle, and (1, -2) is inside the circle. If the radius, r, is an
integer, how many possible values are there for r?

does inside the circle means not on the circle ?

if no then (5,7) if lies on the circle then we should consider that point also.

than also total is 5

Please clarify and correct where m i wrong ?

Regards
SG
Senior Manager  Joined: 13 Jun 2013
Posts: 271
Re: The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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smartyguy wrote:
The center of a circle is (5, -2). (5, 7) is outside the circle, and (1, -2) is inside the circle. If the radius, r, is an
integer, how many possible values are there for r?

does inside the circle means not on the circle ?

if no then (5,7) if lies on the circle then we should consider that point also.

than also total is 5

Please clarify and correct where m i wrong ?

Regards
SG

hi, the situation mentioned in the question can be visualized in the following manner. i hope it helps.
Attachments sol.jpg [ 7.82 KiB | Viewed 6846 times ]

Intern  Joined: 11 Apr 2015
Posts: 32
Location: Germany
Concentration: General Management, Entrepreneurship
GPA: 3.1
WE: Project Management (Energy and Utilities)
Re: The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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2
r must be greater than 4 and smaller than 9, hence r=5,6,7 or 8. Answer A
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Re: The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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The radius can be 5,6,7 or 8. All these cases satisfy the two given conditions.
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Originally posted by sasyaharry on 06 Jul 2017, 13:31.
Last edited by sasyaharry on 06 Jul 2017, 17:06, edited 1 time in total.
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Location: India
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Re: The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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3
3
Given data :
R, the radius of the circle has to be an integer
Center of the circle (5,-2)
Point inside the circle (1,-2)
Point outside the circle (5,7)

Formula used :
Distance between 2 points (x1,y1) and (x2,y2) is $$\sqrt{(x1-x2)^2 + (y1-y2)^2}$$

Since a point inside the circle is (1,-2).
The distance from the center of the circle is $$\sqrt{(5-1)^2 + (-2+2)^2}$$(which is equal to 4)
The point outside the circle is (5,7)
The distance from the center of the circle is $$\sqrt{(5-5)^2 + (7+2)^2}$$(which is equal to 9)

Since we have found out the range of the radius which is 4 < R < 9
We have four values for R(5,6,7,8) (Option A)
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CEO  V
Joined: 12 Sep 2015
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The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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anik89 wrote:
The center of a circle is (5, -2). (5, 7) is outside the circle, and (1, -2) is inside the circle. If the radius, r, is an
integer, how many possible values are there for r?
(A) 4
(B) 5
(C) 6
(D) 7
(E) 8

The center of a circle is (5, -2)
As we can see from the image below, there are infinitely many circles that have their center at (5, -2) (1, -2) is INSIDE the circle
We can quickly determine that the distance from (1, -2) to the circle's center (5, -2) is 4 units... So a circle with a radius of 4 would PASS THROUGH the point (1, -2).
Since (1, -2) is INSIDE the circle, we know that the radius of the circle must be GREATER THAN 4 (5, 7) is OUTSIDE the circle
The distance from (5, 7) to the circle's center (5, -2) is 9 units... So a circle with a radius of 9 would PASS THROUGH the point (5, 7).
Since (5, 7) is OUTSIDE the circle, we know that the radius of the circle must be LESS THAN 9

So, we now have lower and upper limits of the radius.
The radius of the circle is GREATER THAN 4 and LESS THAN 9
In other words, 4 < r < 9

Since the radius, r, is an INTEGER, there are only four possible values of r.
r can equal 5, 6, 7, or 8

Cheers,
Brent
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Originally posted by GMATPrepNow on 25 Oct 2017, 10:19.
Last edited by GMATPrepNow on 16 Apr 2018, 12:23, edited 1 time in total.
VP  D
Joined: 09 Mar 2016
Posts: 1274
The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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pushpitkc wrote:
Given data :
R, the radius of the circle has to be an integer
Center of the circle (5,-2)
Point inside the circle (1,-2)
Point outside the circle (5,7)

Formula used :
Distance between 2 points (x1,y1) and (x2,y2) is $$\sqrt{(x1-x2)^2 + (y1-y2)^2}$$

Since a point inside the circle is (1,-2).
The distance from the center of the circle is $$\sqrt{(5-1)^2 + (-2+2)^2}$$(which is equal to 4)
The point outside the circle is (5,7)
The distance from the center of the circle is $$\sqrt{(5-5)^2 + (7+2)^2}$$(which is equal to 9)

Since we have found out the range of the radius which is 4 < R < 9
We have four values for R(5,6,7,8) (Option A)

Hi pushpitkc,
i have one technical question $$\sqrt{(5-1)^2 + (-2+2)^2}$$(which is equal to 4)

can you expand it how you got 4 ... after taking square root i get this (5-1) + (2+2) which is 8 thank you Board of Directors V
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The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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dave13 wrote:
Hi pushpitkc,
i have one technical question $$\sqrt{(5-1)^2 + (-2+2)^2}$$(which is equal to 4)

can you expand it how you got 4 ... after taking square root i get this (5-1) + (2+2) which is 8 thank you Hey dave13 ,

$$\sqrt{(a)^2 + (b)^2}$$ is not equal to $$a + b$$

You should always solve the equation first (meaning add $$a^2$$ and $$b^2$$) and then take the square root.

Does that make sense?
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Re: The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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abhimahna wrote:
dave13 wrote:
Hi pushpitkc,
i have one technical question $$\sqrt{(5-1)^2 + (-2+2)^2}$$(which is equal to 4)

can you expand it how you got 4 ... after taking square root i get this (5-1) + (2+2) which is 8 thank you Hey dave13 ,

$$\sqrt{(a)^2 + (b)^2}$$ is not equal to $$a + b$$

You should always solve the equation first (meaning add $$a^2$$ and $$b^2$$) and then take the square root.

Does that make sense?

many thanks abhimahna yes it make totally perfect sence $$\sqrt{(5-1)^2 + (-2+2)^2}$$(which is equal to 4)

so i get $$\sqrt{(4)^2 + (0)^2}$$

$$4 + 0$$ = 4 fantastic Senior Manager  P
Joined: 10 Apr 2018
Posts: 267
Location: United States (NC)
Re: The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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Bunuel,
Can we tag this question to Co-ordinate Geometry.

Thanks
Probus
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Probus

~You Just Can't beat the person who never gives up~ Babe Ruth
Math Expert V
Joined: 02 Sep 2009
Posts: 55804
Re: The center of a circle is (5, -2). (5, 7) is outside the circle,  [#permalink]

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Probus wrote:
Bunuel,
Can we tag this question to Co-ordinate Geometry.

Thanks
Probus

_________________
Done. Thank you.
_________________ Re: The center of a circle is (5, -2). (5, 7) is outside the circle,   [#permalink] 12 Jan 2019, 03:30
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