Last visit was: 20 Jul 2024, 23:49 It is currently 20 Jul 2024, 23:49
Toolkit
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
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.
Request Expert Reply

# What is the value of x?

SORT BY:
Tags:
Show Tags
Hide Tags
Intern
Joined: 18 Nov 2013
Posts: 44
Own Kudos [?]: 231 [6]
Given Kudos: 17
GMAT Club Legend
Joined: 12 Sep 2015
Posts: 6804
Own Kudos [?]: 30843 [3]
Given Kudos: 799
Location: Canada
Intern
Joined: 24 Aug 2015
Posts: 39
Own Kudos [?]: 26 [1]
Given Kudos: 25
Location: Spain
Concentration: General Management, Technology
GMAT 1: 750 Q49 V42
GPA: 3.5
WE:Management Consulting (Consulting)
Manager
Joined: 11 Sep 2013
Posts: 96
Own Kudos [?]: 261 [0]
Given Kudos: 26
Re: What is the value of x? [#permalink]
harish1986 wrote:
What is the value of x?

1) $$3x^2-8x-35=0$$
2) $$x^2 - 3x=7x-25$$

2) [m]x^2 - 3x=7x-25 => x = 5 => SUFFICIENT

OA: B
Manager
Joined: 01 Jan 2015
Posts: 56
Own Kudos [?]: 477 [0]
Given Kudos: 14
What is the value of x? [#permalink]
harish1986 wrote:
What is the value of x?

1) $$3x^2-8x-35=0$$
2) $$x^2 - 3x=7x-25$$

A quadratic can have at most 2 real roots, 1 real root with multiplicity of 2, or 0 real roots. To check whether the quadratic has real roots, approximate the discriminant,$$\sqrt{b^2-4*a*c}$$, to see if it is non-negative. The product of the real roots of a quadratic, $$a*x^2+b*x+c = 0$$, is given by $$\frac{c}{a}.$$ To establish sufficiency this quadratic should have one real root with multiplicity of 2. To check quickly whether the quadratic has 1 root, check first to see if b is an integer and then check to see if $$\sqrt{\frac{c}{a}}$$ is rational. If it is easy to calculate the discriminant and it is zero, then it will have one root and checking whether $$\sqrt{\frac{c}{a}}$$ is rational is unnecessary.

(Statement 1): In this statement c=-35 and a=3 --> $$\sqrt{\frac{-35}{3}}$$ = non-rational number. This statement is insufficient

(Statement 2): $$x^2 - 3x=7x-25$$ --> $$x^2-10*x+25=0.$$ In this statement c=25 and a=1 --> $$\sqrt{\frac{25}{1}}$$ = rational number. This statement is sufficient. Also since the discriminant is zero, this statement is sufficient. Correct answer choice is B.

Originally posted by bhaskar438 on 17 Oct 2015, 22:37.
Last edited by bhaskar438 on 19 Oct 2015, 09:54, edited 1 time in total.
Manager
Joined: 01 Jan 2015
Posts: 56
Own Kudos [?]: 477 [0]
Given Kudos: 14
Re: What is the value of x? [#permalink]
Please change the answer from Choice C to Choice B.
Math Expert
Joined: 02 Sep 2009
Posts: 94433
Own Kudos [?]: 642611 [0]
Given Kudos: 86715
Re: What is the value of x? [#permalink]
Expert Reply
bhaskar438 wrote:
Please change the answer from Choice C to Choice B.

_______________
Edited. Thank you.
Current Student
Joined: 01 Dec 2016
Posts: 79
Own Kudos [?]: 59 [0]
Given Kudos: 32
Concentration: Finance, Entrepreneurship
GMAT 1: 650 Q47 V34
WE:Investment Banking (Investment Banking)
Re: What is the value of x? [#permalink]
Easy one! answer is B

You don't need to find the values of the solutions.
By just knowing that (b^2 - 4*a*c) equal zero tells you that answer statement (2) has a unique solution.
statement (1) deos not.
Intern
Joined: 10 Jul 2012
Status:GMAT...one last time for good!!
Posts: 44
Own Kudos [?]: 64 [0]
Given Kudos: 18
Location: India
Concentration: General Management
GMAT 1: 660 Q47 V34
GPA: 3.5
Re: What is the value of x? [#permalink]
harish1986 wrote:
What is the value of x?

1) $$3x^2-8x-35=0$$
2) $$x^2 - 3x=7x-25$$

Discriminant (sqrt(b2-4ac)

D=0; one root,
D<0; no solutions
D=0; 1 solution
D>1; 2 solutions
Re: What is the value of x? [#permalink]
Moderator:
Math Expert
94433 posts