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655-705 (Hard)|   Geometry|      
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What is the ratio of OA to AC? (1) OD is half the length of DC 18 Sep 2018, 22:02
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Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

55% (hard)

Question Stats:

63% (02:19) correct 38% (02:47) wrong based on 80 sessions

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What is the ratio of OA to AC? (Assume O is the center of the circle)

(1) OD is half the length of DC
(2) The area of ADC is 20.


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A
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What is the ratio of OA to AC? (1) OD is half the length of DC 21 Sep 2018, 04:47
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Bunuel

What is the ratio of OA to AC?

(1) OD is half the length of DC
(2) The area of ADC is 20.


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Question stem:- OA:AC=?

St1:- OD is half the length of DC

Please refer the enclosed diagram,

Radius, OC=OA=3x

Applying Pythagoras theorem in the triangle OAD, \(AD=2\sqrt{2}x\)
Again, Applying Pythagoras theorem in the triangle ADC, \(AC=2\sqrt{3}x\)

Now ratio of OA to AC can be determined.

Sufficient.

St2:- The area of ADC is 20.

No information is provided on the measure of AD and DC.

Insufficient.

Ans. (A)
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What is the ratio of OA to AC? (1) OD is half the length of DC 23 Sep 2018, 01:01
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Bunuel, Do we have to consider that O is Center?
if O is not the center, it seems E

Bunuel

What is the ratio of OA to AC?

(1) OD is half the length of DC
(2) The area of ADC is 20.


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What is the ratio of OA to AC? (1) OD is half the length of DC 23 Sep 2018, 01:05
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I think we must consider point 'O' centre of the circle in the same way we do consider Angle ADC 90 degree.

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What is the ratio of OA to AC? (1) OD is half the length of DC 23 Sep 2018, 01:08
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I couldn't get you, We can still have angle ADC= 90, without O as Center.

PKN
I think we must consider point 'O' centre of the circle in the want we do consider Angle ADC 90 degree.

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What is the ratio of OA to AC? (1) OD is half the length of DC 23 Sep 2018, 01:32
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gmatbusters
I couldn't get you, We can still have angle ADC= 90, without O as Center.

PKN
I think we must consider point 'O' centre of the circle in the want we do consider Angle ADC 90 degree.

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We can't assume that OC is radius because it is not mentioned anywhere in the statement. The trap in DS problem is that if it is not given we can't assume.

If it's mentioned that OC is radius then the answer will be A .

Therefore it is E.
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What is the ratio of OA to AC? (1) OD is half the length of DC 23 Sep 2018, 02:10
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gmatbusters
I couldn't get you, We can still have angle ADC= 90, without O as Center.

PKN
I think we must consider point 'O' centre of the circle in the want we do consider Angle ADC 90 degree.

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My reasoning:-
1) Notice a square symbol at point D. And we say angle ADC or Angle ADO is 90 degree

In the same way,

2) Notice "a BOLD DOT mark" at point O. We can say point 'O' the centre of the circle.
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What is the ratio of OA to AC? (1) OD is half the length of DC 23 Sep 2018, 03:22
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gmatbusters
Bunuel, Do we have to consider that O is Center?
if O is not the center, it seems E

Bunuel

What is the ratio of OA to AC?

(1) OD is half the length of DC
(2) The area of ADC is 20.


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Fixed. Thank you.
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What is the ratio of OA to AC? (1) OD is half the length of DC 03 Mar 2021, 05:30
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