Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 49251

In the figure shown, point O is the center of the circle and points B,
[#permalink]
Show Tags
21 Apr 2015, 05:49
Question Stats:
48% (01:42) correct 52% (02:23) wrong based on 163 sessions
HideShow timer Statistics



Retired Moderator
Joined: 06 Jul 2014
Posts: 1244
Location: Ukraine
Concentration: Entrepreneurship, Technology
GMAT 1: 660 Q48 V33 GMAT 2: 740 Q50 V40

Re: In the figure shown, point O is the center of the circle and points B,
[#permalink]
Show Tags
21 Apr 2015, 08:38
Bunuel wrote: Attachment: GMAT1.jpg In the figure shown, point O is the center of the circle and points B, C, and D lie on the circle. If the segment AB is equal to the length of line segment OC, what is the degree measure of angle BAO? (1) The degree measure of angle COD is 60 (2) The degree measure of angle BCO is 40 Kudos for a correct solution.1) Insufficient 2) We know that BO=CO because they are radiuses. So we know that angle OCB equal to angle BCO and equal to 40 degree angle ABO equal 180  CBO = 180  40 = 140 degrees AB = OC = BO so triangle ABO isosceles, so angles BAO and BOA are equal and equal to 180  ABO = 180  140 = 40 / 2 = 20 degrees Sufficient. Answer is B
_________________
Simple way to always control time during the quant part. How to solve main idea questions without full understanding of RC. 660 (Q48, V33)  unpleasant surprise 740 (Q50, V40, IR3)  antidebrief



Manager
Joined: 14 Mar 2014
Posts: 147

Re: In the figure shown, point O is the center of the circle and points B,
[#permalink]
Show Tags
21 Apr 2015, 21:21
A) If COD = 60, then we would end COD as equilateral triangle.  Insufficient. B) If BCO = 40, then In BCO OC = OB(Radius) Thus angles CBO= OCB = 40. We know that angle in a straight line = 180. Thus ABC line make 180. Thus ABO = 140. Triangle ABO AB = OB , thus angle BAO = BOA . Thus B alone is sufficient to find the angle BAO . B Alone is sufficient
_________________
I'm happy, if I make math for you slightly clearer And yes, I like kudos ¯\_(ツ)_/¯



Current Student
Status: GMAT Date: 10/08/15
Joined: 17 Jul 2014
Posts: 89
Location: United States (MA)
Concentration: Human Resources, Strategy
GPA: 3.5
WE: Human Resources (Consumer Products)

Re: In the figure shown, point O is the center of the circle and points B,
[#permalink]
Show Tags
22 Apr 2015, 02:13
Bunuel wrote: Attachment: GMAT1.jpg In the figure shown, point O is the center of the circle and points B, C, and D lie on the circle. If the segment AB is equal to the length of line segment OC, what is the degree measure of angle BAO? (1) The degree measure of angle COD is 60 (2) The degree measure of angle BCO is 40 Kudos for a correct solution.Hello, Here is a detailed explanation of how I approached it: Step 1: Lets mark all lines that will be equal based on the question stem• AB =OB=OC [OB and OC are radii lines] • Applying similar triangle theories, we know that angle opposite to equal sides will be equal. This gives us: o Angle CBO = angle BCO  i o Angle BOA = angle BAO iiNow let’s move to the statements Statement 1: If angle COD is 60 degrees then angle COA = 18060=120. But we don’t know how is this 120 degrees split between angle COB and angle BOA. So, insufficientStatement 2: Angle BCO is 40 degrees Using i we know that angle CBO is 40 too. Angle ABO is 18040 = 140 degrees [ they are on a straight line] Using ii we know that the remaining 40 degrees should be equally divided between angle BOA and angle BAO. i.e. 20 degree each. Hence statement 2 is sufficient > BThanks, aimtoteach **Please give Kudos if the explanation was helpful**
_________________
Thanks, aimtoteach
~~~~~~~~~~~~~~~~~
Please give Kudos if you find this post useful.



Manager
Joined: 25 Jan 2015
Posts: 104
Location: United States

Re: In the figure shown, point O is the center of the circle and points B,
[#permalink]
Show Tags
22 Apr 2015, 02:56
DSolution in the attached file
Attachments
Circle.pdf [115.74 KiB]
Downloaded 118 times



Intern
Joined: 06 Aug 2014
Posts: 18

Re: In the figure shown, point O is the center of the circle and points B,
[#permalink]
Show Tags
22 Apr 2015, 03:04
Answer should be D.
Statement1 is sufficient <COD = 60 so < COA = 120
Now BO=OC => <OCB = < CBO let it be 2X
<CBO is exterior angle for <BAO and <BOA => < CBO = <BAO + <BOA => <BAO = <BOA = X
Since <OCB = < CBQ = 2X => <COB = 180  4X
Now <COB+<BOA = 120 => 1804X+X = 120 => X = 20 => <BAO = 20



Senior Manager
Joined: 27 Dec 2013
Posts: 262

Re: In the figure shown, point O is the center of the circle and points B,
[#permalink]
Show Tags
22 Apr 2015, 11:23
Yes.. The Answer is D. But really a good brainer. Bunuel wrote: Attachment: GMAT1.jpg In the figure shown, point O is the center of the circle and points B, C, and D lie on the circle. If the segment AB is equal to the length of line segment OC, what is the degree measure of angle BAO? (1) The degree measure of angle COD is 60 (2) The degree measure of angle BCO is 40 Kudos for a correct solution.
_________________
Kudos to you, for helping me with some KUDOS.



Math Expert
Joined: 02 Sep 2009
Posts: 49251

Re: In the figure shown, point O is the center of the circle and points B,
[#permalink]
Show Tags
27 Apr 2015, 03:24
Bunuel wrote: In the figure shown, point O is the center of the circle and points B, C, and D lie on the circle. If the segment AB is equal to the length of line segment OC, what is the degree measure of angle BAO? (1) The degree measure of angle COD is 60 (2) The degree measure of angle BCO is 40 Kudos for a correct solution.Attachment: The attachment GMAT1.jpg is no longer available VERITAS PREP OFFICIAL SOLUTION:That is a complicatedlooking figure. Your instinct might be that you don’t have time to draw it, but these kinds of questions will be designed specifically to thwart our intuition if we attempt to do too much work in our heads. So the first thing to do is draw the figure on our scratch pad, and mark the relationships we’re given. We’re told that segment CO is equal to AB, so we’ll designate that relationship. We’ll also call angle BAO, which we’re asked about, ‘x.’ Now we have the following: Attachment:
GMAT2.jpg [ 18.14 KiB  Viewed 3439 times ]
Fight the impulse to jump to the statements now. In a harder question like this, we’ll benefit from taking more time to derive additional relationships from the question stem. Psychologically, this is often a struggle for testtakers. You’re conscious of your time constraint. You want to work quickly. The trick is to trust that this prestatement investment of time will allow you to evaluate the information provided in the statements more efficiently, ultimately saving time. Now the name of the game is to try to label as much of this figure as we can without introducing a new variable. Notice that segments CO and BO are both radii of the circle, so we know those are equal. Our diagram now looks like this: Attachment:
GMAT3.jpg [ 18.4 KiB  Viewed 3438 times ]
Next, look at triangle ABO. Notice that segments AB and BO are equal. If angles opposite equal angles are equal to each other, we can then designate angle AOB as ‘x’ because it must be equal to angle BAO, as those two angles are opposite sides that are of equal length. Moreover, if the three interior angles of a triangle will sum to 180, the remaining angle, ABO, can be designated 1802x. This gives us the following. Attachment:
GMAT4.jpg [ 18.91 KiB  Viewed 3435 times ]
No reason to stop here. Notice that angles ABO and CBO lie on a line. Angles that lie on a line must sum to 180. If angle ABO is 1802x, then angle CBO must be 2x. Now we have this: Attachment:
GMAT5.jpg [ 19.62 KiB  Viewed 3432 times ]
Analyzing triangle CBO, we see that sides BO and CO are equal, meaning that the angles opposite those sides must be equal. So now we can label angle BCO as ‘2x.’ If angles CBO and BOC sum to 4x, the remaining angle, BOC, must then be 1804x, so that the interior angles of the triangle will sum to 180. Attachment:
GMAT6.jpg [ 19.59 KiB  Viewed 3436 times ]
We’ve got enough at this point that we can very quickly evaluate our statements, However, there is one last interesting relationship. Notice that angle COD is an exterior angle of triangle CAO. An exterior angle, by definition, must be equal to the sum of the two remote interior angles. So, in this case, Angle COD is equal to the sum of angles BCO and BAO. Therefore COD = 2x + x = 3x, which I’ve circled in the figure. (Triangle CAO is outlined in blue in the figure below to more clearly demarcate the exterior angle.) Attachment:
GMAT7.jpg [ 20.77 KiB  Viewed 3437 times ]
That’s a lot of work. Determining all of these relationships will likely take close to two minutes. But watch how quickly we can evaluate our statements if we’ve done all of this preemptive groundwork: Statement 1: Angle COD = 60. We’ve designated angle COD as 3x, so 3x = 60. Clearly we can solve for x. Sufficient. Eliminate BCE. Statement 2: Angle BCO = 40. We’ve designated angle BCO as 2x, so 2x = 40. Clearly we can solve for x. Sufficient. Answer is D. Notice, all of the heavy lifting for this question came before we even so much as glanced at our statements. Takeaway: For a challenging Data Sufficiency question in which you’re given a lot of information in the question stem, the best approach is to spend some time taming the complexity of the problem before examining the statements. When you work out these relationships, try to minimize the number of variables you use when doing so, as this will simplify your calculations once you’re ready to go to the statements. Most importantly, don’t do too much work in your head. There’s no need to rely on the limited bandwidth of your working memory if you have the option of putting everything into a concrete form on your scratch pad.
_________________
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.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Current Student
Status: GMAT Date: 10/08/15
Joined: 17 Jul 2014
Posts: 89
Location: United States (MA)
Concentration: Human Resources, Strategy
GPA: 3.5
WE: Human Resources (Consumer Products)

Re: In the figure shown, point O is the center of the circle and points B,
[#permalink]
Show Tags
27 Apr 2015, 10:10
Great advice Bunuel! I got this one wrong  interestingly, I knew all the properies but got it wrong simply because I jumped straight to the statements. To be honest, if this question comes after the 20th question in GMAT  I dont know how will I be able to control the urge to jump to statements! Bunuel wrote: Bunuel wrote: In the figure shown, point O is the center of the circle and points B, C, and D lie on the circle. If the segment AB is equal to the length of line segment OC, what is the degree measure of angle BAO? (1) The degree measure of angle COD is 60 (2) The degree measure of angle BCO is 40 Kudos for a correct solution. VERITAS PREP OFFICIAL SOLUTION:That is a complicatedlooking figure. Your instinct might be that you don’t have time to draw it, but these kinds of questions will be designed specifically to thwart our intuition if we attempt to do too much work in our heads. So the first thing to do is draw the figure on our scratch pad, and mark the relationships we’re given. We’re told that segment CO is equal to AB, so we’ll designate that relationship. We’ll also call angle BAO, which we’re asked about, ‘x.’ Now we have the following: Attachment: GMAT2.jpg Fight the impulse to jump to the statements now. In a harder question like this, we’ll benefit from taking more time to derive additional relationships from the question stem. Psychologically, this is often a struggle for testtakers. You’re conscious of your time constraint. You want to work quickly. The trick is to trust that this prestatement investment of time will allow you to evaluate the information provided in the statements more efficiently, ultimately saving time. Now the name of the game is to try to label as much of this figure as we can without introducing a new variable. Notice that segments CO and BO are both radii of the circle, so we know those are equal. Our diagram now looks like this: Attachment: GMAT3.jpg Next, look at triangle ABO. Notice that segments AB and BO are equal. If angles opposite equal angles are equal to each other, we can then designate angle AOB as ‘x’ because it must be equal to angle BAO, as those two angles are opposite sides that are of equal length. Moreover, if the three interior angles of a triangle will sum to 180, the remaining angle, ABO, can be designated 1802x. This gives us the following. Attachment: GMAT4.jpg No reason to stop here. Notice that angles ABO and CBO lie on a line. Angles that lie on a line must sum to 180. If angle ABO is 1802x, then angle CBO must be 2x. Now we have this: Attachment: GMAT5.jpg Analyzing triangle CBO, we see that sides BO and CO are equal, meaning that the angles opposite those sides must be equal. So now we can label angle BCO as ‘2x.’ If angles CBO and BOC sum to 4x, the remaining angle, BOC, must then be 1804x, so that the interior angles of the triangle will sum to 180. Attachment: GMAT6.jpg We’ve got enough at this point that we can very quickly evaluate our statements, However, there is one last interesting relationship. Notice that angle COD is an exterior angle of triangle CAO. An exterior angle, by definition, must be equal to the sum of the two remote interior angles. So, in this case, Angle COD is equal to the sum of angles BCO and BAO. Therefore COD = 2x + x = 3x, which I’ve circled in the figure. (Triangle CAO is outlined in blue in the figure below to more clearly demarcate the exterior angle.) Attachment: GMAT7.jpg That’s a lot of work. Determining all of these relationships will likely take close to two minutes. But watch how quickly we can evaluate our statements if we’ve done all of this preemptive groundwork: Statement 1: Angle COD = 60. We’ve designated angle COD as 3x, so 3x = 60. Clearly we can solve for x. Sufficient. Eliminate BCE. Statement 2: Angle BCO = 40. We’ve designated angle BCO as 2x, so 2x = 40. Clearly we can solve for x. Sufficient. Answer is D. Notice, all of the heavy lifting for this question came before we even so much as glanced at our statements. Takeaway: For a challenging Data Sufficiency question in which you’re given a lot of information in the question stem, the best approach is to spend some time taming the complexity of the problem before examining the statements. When you work out these relationships, try to minimize the number of variables you use when doing so, as this will simplify your calculations once you’re ready to go to the statements. Most importantly, don’t do too much work in your head. There’s no need to rely on the limited bandwidth of your working memory if you have the option of putting everything into a concrete form on your scratch pad.
_________________
Thanks, aimtoteach
~~~~~~~~~~~~~~~~~
Please give Kudos if you find this post useful.



NonHuman User
Joined: 09 Sep 2013
Posts: 8095

Re: In the figure shown, point O is the center of the circle and points B,
[#permalink]
Show Tags
13 Apr 2018, 03:49
Hello from the GMAT Club BumpBot! Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up  doing my job. I think you may find it valuable (esp those replies with Kudos). Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
GMAT Books  GMAT Club Tests  Best Prices on GMAT Courses  GMAT Mobile App  Math Resources  Verbal Resources




Re: In the figure shown, point O is the center of the circle and points B, &nbs
[#permalink]
13 Apr 2018, 03:49






