Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

DS questions that stumped me from GMATPrep2 [#permalink]
07 Dec 2011, 10:43

00:00

A

B

C

D

E

Difficulty:

5% (low)

Question Stats:

56% (01:15) correct
44% (01:28) wrong based on 9 sessions

I took my first GmatPrep today after studying Quant for a month(Working on a 3month plan suggested by gmatclub experts). I haven't touched Verbal yet and my score was 660 (Q49V31) although i was a little disturbed about my Verbal score since i expected better, i was pretty surprised how getting 13 questions wrong in Quant got me to 49. But since GMAT is adaptive i guessed its possible. Anyways, i reworked the incorrect questions after the exam and cracked a few of them, however there are a few others that just stumped me completely even after giving them a 2nd shot.

1. If ab!=0 and point (-a,b) and (-b,a) are in the same quadrant ,does point (-x,y) lie in this quadrant? i) xy>0 ii) ax>0

There are a few others coming up..Please let me know if I made a rookie mistake by posting these here when it should be in some other forum category, I searched a lot couldn't really find any other suitable place. Thanks

1. If ab!=0 and point (-a,b) and (-b,a) are in the same quadrant ? i) xy>0 ii) ax>0

I think you've missed part of the question here - I think the question says:

If (-a, b) and (-b, a) are in the same quadrant, is the point (-x, y) in the same quadrant as (-a, b)? 1) xy > 0 2) ax > 0

If two points are in the same quadrant, then their x-coordinates have the same sign, and their y-coordinates have the same sign. So from the information that (-a, b) and (-b, a) are in the same quadrant, we learn that a and b have the same sign (either by looking at x-coordinates or at y-coordinates). So we know that a and b are either both positive or both negative, and that the point (-a, b) thus has one negative coordinate and one positive coordinate. The problem is we don't know which coordinate is positive, and which negative; it could be (+, -) or it could be (-, +).

From Statement 1, we learn that x and y have the same sign. Thus the point (-x, y) has coordinates of opposite signs. This point could be (+, -) or (-, +), so we don't know if it's in the same quadrant as (-a, b).

Statement 2 doesn't mention y at all, so cannot be sufficient, since we need to know about the sign of y.

Combining the two statements we know a and b have the same sign (from the stem), a and x have the same sign (from Statement 2) and x and y have the same sign (from Statement 1). So a, b, x and y all have the same sign. Thus the x-coordinates of (-a, b) and (-x, y) have the same sign, as do their y-coordinates, and the two points must be in the same quadrant. The answer is C. _________________

Nov 2011: After years of development, I am now making my advanced Quant books and high-level problem sets available for sale. Contact me at ianstewartgmat at gmail.com for details.

Re: DS questions that stumped me from GMATPrep2 [#permalink]
18 Dec 2011, 15:48

(-a, b) and (-b, a) are in the same quadrant. Is the point (-x, y) in the same quadrant as point (-a, b)?

(1) xy > 0 (2) ax > 0

From the information that (-a, b) and (-b, a) are in the same quadrant, it can be determined that (-a, b) is in either quadrant II or quadrant IV. If (x, y) and (a, b) are in the same exact quadrant, they will have the same sign and (-x, y) will be in the same quadrant as (-a, b)'s.

(1) xy > 0

(x, y) is in quadrant I or quadrant III. (-x, y) is in quadrant II or quadrant IV. No further information is provided about (-a, b).

(2) ax > 0

Point x in (x, y) has the same sign as does point a in (a, b). Since a and b have the same sign, x, a and b have the same sign.

But the sign of point x could be different from, or the same as, the sign of point y. The condition that (x, y) and (a, b) have the same sign, and therefore that (-x, y) and (-a, b) are in the same quadrant, is possible but uncertain.

Combined analysis:

x has the same sign as y x has the same sign as a and b x, y, a and b all have the same sign.

This means (x, y) and (a, b) are in the same quadrant. (-x, y) and (-a, b) are in the same quadrant.

[xyab+xdj]

Last edited by Study1 on 31 Jan 2012, 15:26, edited 3 times in total.

Re: DS questions that stumped me from GMATPrep2 [#permalink]
18 Dec 2011, 17:23

@IanStewart - Nice explanation. kudos to you! _________________

----------------------------------------------------------------------------------------- What you do TODAY is important because you're exchanging a day of your life for it! -----------------------------------------------------------------------------------------

gmatclubot

Re: DS questions that stumped me from GMATPrep2
[#permalink]
18 Dec 2011, 17:23