What is the circumference of circle C ? (1) The radius of circle C is

Question

What is the circumference of circle C ?

(1) The radius of circle C is 2π.
(2) The center of circle C is located at point (7,8) in the xy-plane.

NEW question from GMAT® Official Guide 2019 
(DS06397)

BrentGMATPrepNow · Accepted Answer

Target question :    What is the circumference of circle C ?

Statement 1 : The radius of circle C is  2π .  
Useful formula: circumference = (2π)( radius )
Now that we know the radius is  2π , the circumference = 2π( 2π ) =  4π² 
In other words, the answer to the target question is   the circumference of circle C is 4π²  
Since we can answer the  target question  with certainty, statement 1 is SUFFICIENT

Statement 2 : The center of circle C is located at point (7,8) in the xy-plane. 
 https://i.imgur.com/NpDanAQ.png 
Notice that there are infinitely many different circles that can have their center at (7,8)
This means there are infinitely many different answers to the  target question  
Since we cannot answer the  target question  with certainty, statement 2 is NOT SUFFICIENT

Answer: A

Cheers,
Brent

EgmatQuantExpert · Answer

Solution

To find:  
 • The circumference of the circle C

Approach and Working:  
To find out the circumference of the circle C, we need to know
 • The length of the radius of the circle

Analysing Statement 1  
 • As per the information given in statement 1, the radius of circle C is 2π
• As we know the length of the radius, we can find out the circumference of the circle

Hence, statement 1 is sufficient to answer the question

Analysing Statement 2  
 • As per the information given in statement 2, the center of circle C is at (7,8) in the xy plane
• However, to find the length of the radius of the circle, we need to know the coordinate of at least one point which is on the circumference of the circle

Hence, statement 2 is not sufficient to answer

Hence, the correct answer is option A.

Answer: A

ankitsaroha · Answer

Answer is A.

Circumference = 2πr
We need only radius of the circle.

Statement 1 tells us the radius so it is sufficient.
Statement 2 only tells us the centre. The radius can have any value.
Insufficient.

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iskov · Answer

A most be the right answer since:

1. gives radius and therefore we can find the circumference.

2. is a tautological

alphastallion · Answer

From Stmt 1:We have been given directly ,radius of the circle from which we can find the circumference ,it straight forward answer.

From Stmt 2:The center of circle C is located at point (7,8) in the xy-plane,which can be substituted in equation to circle formula (x-a)^2 +(y-b)^2 = r^2.
(x-7)^2+(y-8)^2=r^2
from where we can expand to find the radius of circle,i think answer should be D.

Antreev · Answer

u substituted a and b with the given values in statement 2.. there is no further given point on the circle which we can substitute in the place of x and y to find r.. this we have one equation and three variables so we cannot find R using statement 2, thus answer is C

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rishab0507 · Answer

Answer A:

to know circumference, we need to know radius : 
Case 1 : gives us radius: so Sufficient
Case 2 : tell us point 7,8 it passes through . So if we draw line from 7,8 to x and y axis we know 2 sides of triangle, 3rd side can be joined from center to origin, i.e 0,0 . We can calculate third side by pythagores theorem , but still it is not the radii.

If questions says that it passes through origin, then we have other point i.e 0,0 and we can say that this hypotenuse is radii, or if questions gives us any other point it passes through or it lies on its surface. Thus it is insufficient

A is only solution

Neena96 · Answer

Hi Brent, is it okay that we dont know the value of 'n' in statement 1 ?

ScottTargetTestPrep · Answer

Solution:

Recall that the circumference of the circle is 2π times the radius of the circle. So if we know (or can determine) the radius, we can determine the circumference of the circle.

Statement One Only:

The radius of circle C is 2π.

Knowing the radius of the circle is sufficient to determine the circumference of the circle.

Statement Two Only:

The center of circle C is located at point (7,8) in the xy-plane.

Knowing only the location of the center of the circle does not allow us to determine the circumference of the circle. Since we neither know nor can determine the radius of the circle, we can’t determine the circumference of the circle.

Answer: A

nermeendhuca · Answer

We still don't know what "n" is... doesn't that mean the answer can't be A?

siriusly · Answer

Oops a mistake I also made.. it is pi, not n

CrackverbalGMAT · Answer

SOLUTION:

Statement (1) -Using the given radius, Area can be calculated.(Sufficient)

Statement (2)-Using the coordinate of the center, we DO NOT have enough information for the radius.
There can be infinite circles that can be drawn with (7,8).(Insufficient)
Hence (OPTION A)

Hope this helps

Devmitra Sen(Math)

GMATinsight · Answer

Answer: Option A

Video solution by  GMATinsight

https://www.youtube.com/watch?v=M2HNnSEc86A

avigutman · Answer

Video solution from Quant Reasoning: Subscribe for more: https://www.youtube.com/QuantReasoning? ... irmation=1 https://www.youtube.com/watch?v=_48ytiI7wQ0

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What is the circumference of circle C ? (1) The radius of circle C is

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