It is currently 23 Jun 2017, 07:09

### GMAT Club Daily Prep

#### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# M24 #12 - formatting error

Author Message
CIO
Joined: 02 Oct 2007
Posts: 1218
Re: M24 #12 - formatting error [#permalink]

### Show Tags

09 Feb 2010, 09:03
Wow. Bunuel, fantastic explanation, as always .
Bunuel wrote:
zoinnk wrote:
Do lines $$y = ax^2 + b$$ and $$y = cx^2 + d$$ cross?

1. $$a = -c$$
2. $$b \gt d$$

[Reveal] Spoiler: OA
E

Source: GMAT Club Tests - hardest GMAT questions

What am I supposed to do w/ #2?

I'd like to comment on this one:

First of all: equations given ARE NOT ...

_________________

Welcome to GMAT Club!

Want to solve GMAT questions on the go? GMAT Club iPhone app will help.
Result correlation between real GMAT and GMAT Club Tests
Are GMAT Club Test sets ordered in any way?

Take 15 free tests with questions from GMAT Club, Knewton, Manhattan GMAT, and Veritas.

GMAT Club Premium Membership - big benefits and savings

Intern
Joined: 06 Feb 2011
Posts: 2
Re: M24 #12 - formatting error [#permalink]

### Show Tags

11 Feb 2011, 07:20
GMAT exams are only based on real numbers.

If they allowed imaginary numbers that would only make the math more complex. Get it?!?
Senior Manager
Joined: 01 Nov 2010
Posts: 288
Location: India
Concentration: Technology, Marketing
GMAT Date: 08-27-2012
GPA: 3.8
WE: Marketing (Manufacturing)
Re: M24 #12 - formatting error [#permalink]

### Show Tags

11 Feb 2011, 08:13
A would have been the answer provided a=c not equal to zero
since, no condition is given hence, we cant its A.
and by using both statement together also we cant say whether it will cross or not.
if constants are not equal to zero, then the curve will cross each other.
if constants(a&C) are zero, then it is line with different value. wont cross each other.
and if, constant (all) are zero they will over lap.

so, the best answer is E.
_________________

kudos me if you like my post.

Attitude determine everything.
all the best and God bless you.

Intern
Joined: 16 Jan 2011
Posts: 6
Schools: Arizona State University
Re: M24 #12 - formatting error [#permalink]

### Show Tags

13 Feb 2011, 00:35
Please explain as to how did you get from 2ax^2 + (b-d) = 0 ----> to d=0 - 8a(b-d) >= 0....
and from (a-c)x^2 +(b-a) = 0 -----> to d = 0 - 4(a-c)(b-d) >= 0

This would help me see what I am missing. I understood the explanation but stuck at how the above equation for 'd' was derived.
Math Expert
Joined: 02 Sep 2009
Posts: 39598
Re: M24 #12 - formatting error [#permalink]

### Show Tags

13 Feb 2011, 03:13
saswani wrote:
Please explain as to how did you get from 2ax^2 + (b-d) = 0 ----> to d=0 - 8a(b-d) >= 0....
and from (a-c)x^2 +(b-a) = 0 -----> to d = 0 - 4(a-c)(b-d) >= 0

This would help me see what I am missing. I understood the explanation but stuck at how the above equation for 'd' was derived.

Second d (red part) stands here for the discriminant of a quadratic expression not the variable d.

Check this for more: math-coordinate-geometry-87652.html (Parabola chapter)
_________________
Intern
Joined: 16 Jan 2011
Posts: 6
Schools: Arizona State University
Re: M24 #12 - formatting error [#permalink]

### Show Tags

13 Feb 2011, 23:38
Ahhhh i see...this makes more sense...thanks so much Bunuel!!!
Intern
Joined: 22 Dec 2010
Posts: 6
Re: M24 #12 - formatting error [#permalink]

### Show Tags

14 Feb 2011, 06:33
These are 2 paraboles.
Statement 1 (one of the paraboles is inverted depending on a negative or positive) ==> alone insufficient
Statement 2 Parobole 1 crosses 0 above Parabole 2 ==> alone insufficient
They would cross each other if a was negative. But as this information is not there ==> both statement insufficient

E
Manager
Joined: 02 Feb 2012
Posts: 204
Location: United States
GMAT 1: 770 Q49 V47
GPA: 3.08
Re: M24 #12 - formatting error [#permalink]

### Show Tags

16 Feb 2012, 18:08
I answered C, which upon further thinking was a careless mistake. To answer the question I tentatively drew out different scenarios for each equation.

With statement 1, the parabola can cross or not cross, it all depends on b and d (insufficient)

With statement 2, we don't have information on a or c, so they can still cross or not cross (insufficient)

When combining to the two statements, I made the mistake of assuming that a was positive and c was negative, which given statement 2, the two lines would not cross. I stupidly forgot about the opposite situation, where statement 1 would still be satisfied, but would give a different result.

Silly mistake.

Manager
Joined: 25 Aug 2011
Posts: 196
Location: India
GMAT 1: 730 Q49 V40
WE: Operations (Insurance)
Re: M24 #12 - formatting error [#permalink]

### Show Tags

27 Feb 2012, 23:04
Hi I am getting c. Please see the attached image.. please expl this solution is not why this solution is not correct
Attachments

equations intersect.jpg [ 23.83 KiB | Viewed 1763 times ]

equations intersect.jpg [ 26.78 KiB | Viewed 1763 times ]

Math Expert
Joined: 02 Sep 2009
Posts: 39598
Re: M24 #12 - formatting error [#permalink]

### Show Tags

27 Feb 2012, 23:21
1
KUDOS
Expert's post
devinawilliam83 wrote:
Hi I am getting c. Please see the attached image.. please expl this solution is not why this solution is not correct

Please read the solutions above with algebraic as well as number plugging approaches showing that answer is E, not C.

The problem with your reasoning is that the case you've given is not the only possible one, there are the cases when the graphs do not intersect.

Consider the graphs y=x^2+1 and y=-x^2 to get answer NO:
Attachment:

1.gif [ 4.4 KiB | Viewed 1760 times ]

Consider the graphs y=-x^2+1 and y=x^2 to get answer YES:
Attachment:

2.gif [ 5.18 KiB | Viewed 1760 times ]

Hope it's clear.
_________________
Manager
Joined: 25 Aug 2011
Posts: 196
Location: India
GMAT 1: 730 Q49 V40
WE: Operations (Insurance)
Re: M24 #12 - formatting error [#permalink]

### Show Tags

27 Feb 2012, 23:42
Yes I missed that .. Thanks
Manager
Joined: 05 Sep 2012
Posts: 78
Re: M24 #12 - formatting error [#permalink]

### Show Tags

15 Feb 2013, 06:17
Gr8 question.

E for me because the signs a, b, c, d are unknown even after combining both the conditions.

If a or c would had been given positive, then the answer could be determined.
Intern
Joined: 30 May 2011
Posts: 18
Re: M24 #12 - formatting error [#permalink]

### Show Tags

15 Feb 2013, 10:09
I thought the in geometry definition, parabolas are not consider lines.
Manager
Joined: 20 Oct 2013
Posts: 76
Location: United States
Concentration: General Management, Real Estate
Re: M24 #12 - formatting error [#permalink]

### Show Tags

21 Apr 2014, 06:01
2 lines cross when there exists x so that (a-c)x^2=d-b (*)
1) a=-c: don't mention anything about the right side of (*) -> insufficient
2) b>d: if a<c: (*) has at least one root; if a>c: no root -> insufficient
Combine 2 stats: still insufficient coz we don't know whether a>c or not

Choose E
Re: M24 #12 - formatting error   [#permalink] 21 Apr 2014, 06:01

Go to page   Previous    1   2   [ 34 posts ]

Similar topics Replies Last post
Similar
Topics:
M24-12-Do graphs y=ax2+b a 1 15 May 2013, 01:57
6 M24 Q 33 19 27 Mar 2014, 06:17
14 M24 Q 24 19 06 Dec 2013, 20:17
8 M24#34 19 01 May 2014, 22:09
16 M24 #4 24 02 Jul 2013, 11:21
Display posts from previous: Sort by

# M24 #12 - formatting error

Moderator: Bunuel

 Powered by phpBB © phpBB Group and phpBB SEO Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.