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gmatclub math test13

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gmatclub math test13 [#permalink] New post 30 Mar 2010, 09:53
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

50% (00:00) correct 50% (00:00) wrong based on 7 sessions
please explain.
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Re: gmatclub math test13 [#permalink] New post 30 Mar 2010, 10:50
vaivish1723 wrote:
please explain.

vaivish1723:
You have to understand that not everybody on the forum will have Word-2007. I am work and I cant open you file. It would be better if you can post the question like everybody else.

If you have lots of graphs/pictures and its tough to post it, atleast upload a Word-2003 format file. Most people will be able open the file.
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Re: gmatclub math test13 [#permalink] New post 30 Mar 2010, 10:54
*** think about the distance between eyes, shortest will be the distance measured along the nose and the longest will be distance measured around the back of head.

st 1) angle adb is acute - as length AB is < pi , this says that point D will not be in between AB where AB is the shortest distance around circle between points AB. Not sufficient

st 2) angle adb > angle cad .. here we will get 2 results, if D is in between AB where AB is the shortest distance around circle between points AB then x<y and if D is outside the shortest distance between AB, then x>y
Not sufficient

combining we know that D is not in between AB where AB is the shortest distance around circle between points AB.
so x>y

C

Last edited by chix475ntu on 31 Mar 2010, 12:45, edited 1 time in total.
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Re: gmatclub math test13 [#permalink] New post 31 Mar 2010, 00:23
Stmt 1 - We just know one angle is acute and both arc are less than 22/7 Not Sufficient
Stmt 2 - Arc opposite to angles are always in same ratio as angles. So we know that x > y Hence sufficient

IMO B
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Re: gmatclub math test13 [#permalink] New post 31 Mar 2010, 08:42
Thanks for replies. I will take care next time that i post in V2003.

The OA is C for the posted problem. Please explain.
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Re: gmatclub math test13 [#permalink] New post 31 Mar 2010, 12:46
vaivish1723 wrote:
Thanks for replies. I will take care next time that i post in V2003.

The OA is C for the posted problem. Please explain.


Updated the earlier post.
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Re: gmatclub math test13 [#permalink] New post 31 Mar 2010, 22:33
chix475ntu wrote:
*** think about the distance between eyes, shortest will be the distance measured along the nose and the longest will be distance measured around the back of head.

st 1) angle adb is acute - as length AB is < pi , this says that point D will not be in between AB where AB is the shortest distance around circle between points AB. Not sufficient

st 2) angle adb > angle cad .. here we will get 2 results, if D is in between AB where AB is the shortest distance around circle between points AB then x<y and if D is outside the shortest distance between AB, then x>y
Not sufficient

combining we know that D is not in between AB where AB is the shortest distance around circle between points AB.
so x>y

C


@chix475ntu

Can you please explain in detail.
1.if AB is less than pi then how is it the shortest distance, why not CD which is also less than pi

How do we know that D lies inside and outside the AB

If possible can you post the theory behind the logic you explained above. I have no idea how you made the conclusion

Any help would be highly appreciated
Thanks in advance
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Re: gmatclub math test13 [#permalink] New post 03 Apr 2010, 09:20
Expert's post
Image
So from the question, you should be able to tell that the diagram looks like this:
Image
OR like this:
Image

We are only told that there are 4 points of the circle--so all of them could be in any order. At first, you might think that the 4 points must be in order alphabetically as you go clockwise around the circle. But you cannot make this assumption since the question does not name the circle ABCD. Rather, it says there are 4 points on the circle.

As such, there are two possible situations you need to consider:
1) When the two segments overlap
2) When the two segments do not overlap
Technically, you can even argue the case where CD is inside the bigger segment AB. But then it would be obvious which segment is longer than the other one.

So for the purposes of this GMAT question, you should just consider the overlap and non-overlap situations.

We are told X< pi and Y < pi. Why are they telling us that? Is that pointless additional information or does it actually mean something?


Well, they tell us the radius is 1. We know that the circumference is always some number times pi. It's pi * diameter. So that means the circumference is 2pi. Well, if you imagine an upper half of the circle and lower half of the circle, then each half has length of pi.

We're told that x < pi and y< pi. That means the distance between A and B must be within the upper hemisphere--not exceeding the dotted line in the middle.

Likewise, the distance between C and D must be within the lower hemisphere--not exceeding the dotted line in the middle.

Now, let's look at statement #1: Angle ADB is acute.
This basically tells us that there is NO overlap between the two segments. Why? Look at the overlap image. Clearly, angle ADB is obtuse (>90 degrees). So this overlap diagram is no good if we use statement #1.

Now look at the non-overlap image. Angle ADB is acute.

So really, statement #1 is telling us that there is no overlap. But we still don't know which segment is longer than the other one. We only know there is no overlap.

Now let's look at statement #2: Angle ADB is > angle CAD.

In the Overlap diagram, it's tough to see how this will help us, if at all. We don't know which segment is longer.

In the non-overlap diagram, let's pretend ADB and CAD are the same. Now try to shift point B down-right so ADB > CAD while keeping everything the same. What do you notice? Well, you notice the distance between A and B is getting bigger while the distance between C and D stays the same.

So that's good, but that's only when the segments do not overlap. When they do overlap, we still don't know which segment is longer.

But wait!
What if you combined (1) and (2)?

Statement #1 basically tells us that we are only dealing with the non-overlap diagram.

Statement #2 tells us that for the non-overlap diagrams, one segment is always greater than the other segment.

This is exactly what we're looking for! The question asks "is x>y"? Well, by knowing statement #2 that ADB > CAD---combined with statement #1 that there is NO overlap between the two segments, we know that yes, the length of X > length of Y.

So statement #1 combined with statement #2 is enough to answer the question with only 1 solution. When #1 is no good by itself and #2 is no good by itself, but when combined we can narrow down everything to one correct answer, then the final answer is (C).


Overall, I think this question is more complicated than a typical GMAT question you would see. Even if you got a question this wordy, it would definitely come with a diagram to explain exactly what is going on. I see complications with this question if you swap points C and D--because all the naming of angles become unclear.

In any event, take from this explanation what you can in terms of identifying possible situations and piecing together information.

Hope that helps!
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Re: gmatclub math test13 [#permalink] New post 04 Apr 2010, 01:26
@gmatpill

1. If we exchange point C & D in the overlap diagram (i.e. C lies between A &B and D lies outside) then angle ADB can be acute. So from stmt 1 its not possible to find out if its a case of overlap or non-overlap.

2. As per you explanation in non-overlap case if angle ADB > angle CAD then we know x>Y

here, we cannot be sure about the overlap or non-overlap cases (as per my 1st point)
Even if we are sure and use the theory that arc opposite to angle are in the same ratio as angles, then stmt 2 that one angle is bigger than other, itself is sufficient for conclusion. (as i explained in y previous post)

Can you shed some more light!!!!!
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acute [#permalink] New post 15 Jul 2010, 11:51
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Re: acute [#permalink] New post 15 Jul 2010, 19:57
hi,

1 - Angle ADB is acute, but this doesn't give us any information regarding the angles DBC and DAC that are extended by chord CD. So this is not sufficient to answer the question.

2 - Angles ADB and CAD are equal, thus the chords AB and CD are equal since angles extended by equal chrods (arcs) are equal. Hence 2 alone is sufficient to answer the question.


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Re: acute [#permalink] New post 15 Jul 2010, 21:28
jakolik wrote:
hi,

1 - Angle ADB is acute, but this doesn't give us any information regarding the angles DBC and DAC that are extended by chord CD. So this is not sufficient to answer the question.

2 - Angles ADB and CAD are equal, thus the chords AB and CD are equal since angles extended by equal chrods (arcs) are equal. Hence 2 alone is sufficient to answer the question.


Regards,
Jack


Jack ,
the way i read statement 2 Angle ADB > angle CAD ..did i miss something???

i think the answer is C
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Re: acute [#permalink] New post 15 Jul 2010, 22:32
sorry,

since angle ADB > angle CAD,
then chord corresponding to angle ADB is greater than the chord corresponding to angle CAD.
Thus AB > CD, 2 alone is sufficient.
Hope this is clear now.

regards,
Jack
Re: acute   [#permalink] 15 Jul 2010, 22:32
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