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What is the ratio of OA to AC? (1) OD is half the length of DC

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What is the ratio of OA to AC? (1) OD is half the length of DC  [#permalink]

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New post 18 Sep 2018, 22:02
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A
B
C
D
E

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  45% (medium)

Question Stats:

67% (01:48) correct 33% (02:14) wrong based on 57 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.


Attachment:
image008.jpg
image008.jpg [ 3.19 KiB | Viewed 627 times ]

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Re: What is the ratio of OA to AC? (1) OD is half the length of DC  [#permalink]

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New post 21 Sep 2018, 04:47
1
1
1
Bunuel wrote:
Image
What is the ratio of OA to AC?

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


Attachment:
The attachment image008.jpg is no longer available


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)
Attachments

Circle ratio.PNG
Circle ratio.PNG [ 74.38 KiB | Viewed 477 times ]


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Re: What is the ratio of OA to AC? (1) OD is half the length of DC  [#permalink]

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New post 23 Sep 2018, 01:01
Bunuel, Do we have to consider that O is Center?
if O is not the center, it seems E

Bunuel wrote:
Image
What is the ratio of OA to AC?

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


Attachment:
image008.jpg

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Re: What is the ratio of OA to AC? (1) OD is half the length of DC  [#permalink]

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New post 23 Sep 2018, 01:05
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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Re: What is the ratio of OA to AC? (1) OD is half the length of DC  [#permalink]

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New post 23 Sep 2018, 01:08
I couldn't get you, We can still have angle ADC= 90, without O as Center.

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

Posted from my mobile device

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Re: What is the ratio of OA to AC? (1) OD is half the length of DC  [#permalink]

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New post 23 Sep 2018, 01:32
gmatbusters wrote:
I couldn't get you, We can still have angle ADC= 90, without O as Center.

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

Posted from my mobile device



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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Re: What is the ratio of OA to AC? (1) OD is half the length of DC  [#permalink]

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New post 23 Sep 2018, 02:10
gmatbusters wrote:
I couldn't get you, We can still have angle ADC= 90, without O as Center.

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

Posted from my mobile device


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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Re: What is the ratio of OA to AC? (1) OD is half the length of DC  [#permalink]

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New post 23 Sep 2018, 03:22
gmatbusters wrote:
Bunuel, Do we have to consider that O is Center?
if O is not the center, it seems E

Bunuel wrote:
Image
What is the ratio of OA to AC?

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


Attachment:
image008.jpg

___________________
Fixed. Thank you.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: What is the ratio of OA to AC? (1) OD is half the length of DC &nbs [#permalink] 23 Sep 2018, 03:22
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