It is currently 21 Aug 2017, 10:46

STARTING SOON:

How to get into Stanford GSB

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

DS quadratic question where stat 1 and 2 only give one common root

Author Message
Intern
Joined: 05 Mar 2017
Posts: 1

Kudos [?]: 0 [0], given: 16

DS quadratic question where stat 1 and 2 only give one common root [#permalink]

Show Tags

07 Apr 2017, 13:08
Hi guys,

I have a question to the fundamentals of DS questions.

I know that both DS statements are true and non-contradictory. Thus, I was quite baffled to do a DS question where statement one gives me two quadratic roots: -23, 23, but statement two gives me the quadratic roots: -23, -17.

Could someone explain how this is possible? In my mind, the statements are contradictory then, since only one root is common between the two statements.

The question was from Veritas Prep CAT#2 with Question ID: 07578 (not sure if I'm allowed to post the question here due to copyright).

Thanks!

Kudos [?]: 0 [0], given: 16

 Veritas Prep GMAT Discount Codes Manhattan GMAT Discount Codes Jamboree Discount Codes
Manager
Joined: 17 May 2015
Posts: 191

Kudos [?]: 168 [1] , given: 70

Re: DS quadratic question where stat 1 and 2 only give one common root [#permalink]

Show Tags

07 Apr 2017, 21:24
1
KUDOS
starryskyes wrote:
Hi guys,

I have a question to the fundamentals of DS questions.

I know that both DS statements are true and non-contradictory. Thus, I was quite baffled to do a DS question where statement one gives me two quadratic roots: -23, 23, but statement two gives me the quadratic roots: -23, -17.

Could someone explain how this is possible? In my mind, the statements are contradictory then, since only one root is common between the two statements.

The question was from Veritas Prep CAT#2 with Question ID: 07578 (not sure if I'm allowed to post the question here due to copyright).

Thanks!

Hi starryskyes,

Whatever you have explained above is perfectly fine in a DS question. In such cases, answer would be C.

Let me give you one example from Quant Review(official question).

Is \(y = 6\)

(1) \(y^{2} = 36\)
(2) \(y^{2} - 7y + 6 = 0\)

From st.(1) we have two roots. y = 6 or -6 . Hence, not sufficient.

From st.(2) we get (y-6)(y-1) = 0 => y = 6 or 1. NOT Sufficeint.

Now by combining (1) and (2), we have a unique answer y = 6. Hence, Sufficient. Answer (C)

Hope it helps.

Kudos [?]: 168 [1] , given: 70

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7567

Kudos [?]: 16444 [1] , given: 229

Location: Pune, India
Re: DS quadratic question where stat 1 and 2 only give one common root [#permalink]

Show Tags

09 Apr 2017, 23:40
1
KUDOS
Expert's post
starryskyes wrote:
Hi guys,

I have a question to the fundamentals of DS questions.

I know that both DS statements are true and non-contradictory. Thus, I was quite baffled to do a DS question where statement one gives me two quadratic roots: -23, 23, but statement two gives me the quadratic roots: -23, -17.

Could someone explain how this is possible? In my mind, the statements are contradictory then, since only one root is common between the two statements.

The question was from Veritas Prep CAT#2 with Question ID: 07578 (not sure if I'm allowed to post the question here due to copyright).

Thanks!

You are right - both DS statements are true and non-contradictory. The point is that in this question too, the two statements are true and non contradictory. Let me explain.

Let's simplify:

Question stem: What is x?

Stmnt 1: x is either 23 or -23.
Stmnt 2: x is either -23 or -17.

Now you know that both statements are true. So the value of x has to be one of 23 and -23. It also has to be one of -23 and -17. So the only value that x can take is -23. That will keep both statements true.
In that case, x will be one of 23 and -23 (it is -23) and x will also be one of -23 and -17 (it is -23).

The statements are not contradictory. Using both, we realise that the only value x can take is -23.

I hope this sorts out your doubt!
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for \$199

Veritas Prep Reviews

Kudos [?]: 16444 [1] , given: 229

Re: DS quadratic question where stat 1 and 2 only give one common root   [#permalink] 09 Apr 2017, 23:40
Similar topics Replies Last post
Similar
Topics:
DS PROBLEM 1 09 Nov 2016, 10:22
Verbal question 1 15 Aug 2016, 21:09
SC question 1 18 Jul 2016, 00:14
Not clear with the answer of VP Arithmetic Book -Prob. 76 DS Question 1 16 Jan 2015, 03:53
Display posts from previous: Sort by