GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 17 Feb 2019, 10:01

Close

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.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in February
PrevNext
SuMoTuWeThFrSa
272829303112
3456789
10111213141516
17181920212223
242526272812
Open Detailed Calendar
  • Free GMAT Algebra Webinar

     February 17, 2019

     February 17, 2019

     07:00 AM PST

     09:00 AM PST

    Attend this Free Algebra Webinar and learn how to master Inequalities and Absolute Value problems on GMAT.
  • Valentine's day SALE is on! 25% off.

     February 18, 2019

     February 18, 2019

     10:00 PM PST

     11:00 PM PST

    We don’t care what your relationship status this year - we love you just the way you are. AND we want you to crush the GMAT!

Math Revolution DS Expert - Ask Me Anything about GMAT DS

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

 
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 06 Feb 2019, 07:10
MathRevolution wrote:
[GMAT math practice question]

(number properties) If \(x, y\) are integers, is \((x-y)(x+y)(x^2+y^2)\) an odd number?

1) \(x\) is an odd number
2) \(x-y\) is an odd number


=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

Since \((x-y)(x+y)(x^2+y^2) = x^4-y^4\), the question asks if \(x\) and \(y\) have different parities.

By Condition 2), \(x\) and \(y\) must have different parities since \(x – y\) is an odd number.
Condition 2) is sufficient.

Condition 1)
Since we don’t know whether \(y\) is even or odd, condition 1) is not sufficient.

Therefore, B is the answer.
Answer: B
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 06 Feb 2019, 07:11
[GMAT math practice question]

(inequality) If \(x, y, z\) are positive integers, is \(xyz ≥ 64\)?

\(1) xy ≥ yz ≥ zx ≥ 16\)
\(2) x+y+z=64\)
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

SVP
SVP
User avatar
G
Joined: 18 Aug 2017
Posts: 1775
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
GMAT ToolKit User Premium Member CAT Tests
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 06 Feb 2019, 08:04
fskilnik wrote:
Archit3110 wrote:
MathRevolution wrote:
[GMAT math practice question]

If \(a>b>c>d>0\), is \(d<4\)?

\(1) \frac{1}{c} + \frac{1}{d} > \frac{1}{2}\)
\(2) (\frac{1}{a})+(\frac{1}{b})+(\frac{1}{c})+(\frac{1}{d})=1\)


#2
fraction of 1/a+1/b+1/c+1/d = 1
possible when all a=b=c=d are equal
so in sufficient to say that d<4
IMO A


Hi, Archit3110 !

Please check the parts in red.

Regards,
Fabio.


Fabio
understood thanks.. :)
_________________

If you liked my solution then please give Kudos. Kudos encourage active discussions.

SVP
SVP
User avatar
G
Joined: 18 Aug 2017
Posts: 1775
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
GMAT ToolKit User Premium Member CAT Tests
Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post Updated on: 08 Feb 2019, 04:14
MathRevolution wrote:
[GMAT math practice question]

(inequality) If \(x, y, z\) are positive integers, is \(xyz ≥ 64\)?

\(1) xy ≥ yz ≥ zx ≥ 16\)
\(2) x+y+z=64\)


x,y,z are +ve integers

#1
\(1) xy ≥ yz ≥ zx ≥ 16\)

x=y=z; then only we can have \(1) xy ≥ yz ≥ zx ≥ 16\)
so x=y=z=4 atleast
so \(xyz ≥ 64\); sufficient
#2

\(2) x+y+z=64\)
since x,y,z are + ve integers
so x= 62, y=z=1
so insufficient
IMO A
_________________

If you liked my solution then please give Kudos. Kudos encourage active discussions.


Originally posted by Archit3110 on 06 Feb 2019, 08:12.
Last edited by Archit3110 on 08 Feb 2019, 04:14, edited 1 time in total.
GMATH Teacher
User avatar
G
Status: GMATH founder
Joined: 12 Oct 2010
Posts: 730
Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 06 Feb 2019, 16:32
Archit3110 wrote:
Fabio
understood thanks.. :)

I am glad to know it, Archit3110!

I found your post by coincidence... if you want to "mention" me, so that I know I have a post of yours like this one, do not forget to use my "nickname" fskilnik , please!

("Fabio" is related to someone with no posts, who left this forum in 2009... I have checked that one minute ago.)

Regards and success in your studies!
Fabio.
_________________

Fabio Skilnik :: GMATH method creator (Math for the GMAT)
Our high-level "quant" preparation starts here: https://gmath.net

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 07 Feb 2019, 17:24
MathRevolution wrote:
[GMAT math practice question]

If \(a>b>c>d>0\), is \(d<4\)?

\(1) \frac{1}{c} + \frac{1}{d} > \frac{1}{2}\)
\(2) (\frac{1}{a})+(\frac{1}{b})+(\frac{1}{c})+(\frac{1}{d})=1\)


=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.
The original condition \(a>b>c>d>0\) is equivalent to \(0 < \frac{1}{a} < \frac{1}{b} < \frac{1}{c} < \frac{1}{d}\). The question asks if \(d < 4\). This is equivalent to asking if \(\frac{1}{d} > \frac{1}{4}\).

By condition \(1, \frac{1}{d} > \frac{1}{4}\) since \(\frac{1}{c} < \frac{1}{d}\). So, \(d < 4\). Condition 1) is sufficient.

Condition 2)
Since \(0 < \frac{1}{a} < \frac{1}{b} < \frac{1}{c} < \frac{1}{d}\) and \((\frac{1}{a})+(\frac{1}{b})+(\frac{1}{c})+(\frac{1}{d})=1\), we have \(\frac{1}{a}<\frac{1}{d}\), \(\frac{1}{b}<\frac{1}{d}, \frac{1}{c}<\frac{1}{d}\) and \(\frac{1}{a} +\frac{1}{b} + \frac{1}{c} + \frac{1}{d} < \frac{1}{d} +\frac{1}{d} +\frac{1}{d} + \frac{1}{d} = \frac{4}{d}.\)
Therefore, \(1 < \frac{4}{d}\) and \(d < 4\).
Condition 2) is sufficient.

Therefore, D is the answer.
Answer: D

Note: This question is a CMT4(B) question: condition 1) is easy to work with and condition 2) is hard. For CMT4(B) questions, D is most likely to be the answer.
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 07 Feb 2019, 17:26
[GMAT math practice question]

(absolute value) \(3x+4y=?\)

\(1) 2|x|+3|y|=0\)
\(2) 3|x|+2|y|=0\)
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 08 Feb 2019, 01:38
MathRevolution wrote:
[GMAT math practice question]

(inequality) If \(x, y, z\) are positive integers, is \(xyz ≥ 64\)?

\(1) xy ≥ yz ≥ zx ≥ 16\)
\(2) x+y+z=64\)


=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

Since we have \(3\) variables (\(x, y, z\)) and \(0\) equations, E is most likely to be the answer. So, we should consider each condition on its own first. As condition 1) includes 3 equations, we should consider it first.

Condition 1)
Since \(xy ≥ 16, yz ≥ 16\), and \(zx ≥ 16\), we have \((xyz)^2 ≥ 16^3\) or \(xyz ≥ 64\).
Condition 1) is sufficient.

Condition 2)
If \(x = 20, y = 20\) and \(z = 24\), then \(xyz = 9600 ≥ 64\) and the answer is ‘yes’.
If \(x = 1, y = 1\) and \(z = 62\), then \(xyz = 62 < 64\) and the answer is ‘no’.
Since condition 2) does not yield a unique answer, condition 2) is not sufficient.

Therefore, A is the answer.
Answer: A

This is a CMT(Common Mistake Type) 4(A) question. If a question is from one of the key question areas and C should be the answer, CMT (Common Mistake Type) 4(A) of the VA (Variable Approach) method tells us that we should also check answers A and B.
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 08 Feb 2019, 01:39
[GMAT math practice question]

(function) Does \(f(x)=ax^4+bx^3+cx^2+dx+e\) have (\(x-2\)) as a factor?

\(1) f(2)=0\)
\(2) f(-2)=0\)
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Manager
Manager
avatar
S
Joined: 14 Nov 2015
Posts: 81
Location: India
GPA: 3.7
GMAT ToolKit User Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 08 Feb 2019, 03:57
MathRevolution wrote:
[GMAT math practice question]

(absolute value) \(3x+4y=?\)

\(1) 2|x|+3|y|=0\)
\(2) 3|x|+2|y|=0\)


IMO D

Modulus of any variable is a positive number.

if sum of 2 modulus variables is zero then it means the variable has a value zero

therefore 3x+4y = 0

Hence D
SVP
SVP
User avatar
G
Joined: 18 Aug 2017
Posts: 1775
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
GMAT ToolKit User Premium Member CAT Tests
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 08 Feb 2019, 04:21
MathRevolution wrote:
[GMAT math practice question]

(absolute value) \(3x+4y=?\)

\(1) 2|x|+3|y|=0\)
\(2) 3|x|+2|y|=0\)


#1 :
\(1) 2|x|+3|y|=0\)
whenx=y=0 sufficient
#2
again at x=y=0. sufficient
IMO D
_________________

If you liked my solution then please give Kudos. Kudos encourage active discussions.

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 10 Feb 2019, 17:08
MathRevolution wrote:
[GMAT math practice question]

(absolute value) \(3x+4y=?\)

\(1) 2|x|+3|y|=0\)
\(2) 3|x|+2|y|=0\)


=>
Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

Condition 1)
Since \(|x| ≥ 0, |y| ≥ 0\) and \(2|x| + 3|y| = 0,\) we have \(x = y = 0.\)
Therefore, \(3x + 4y = 0.\)
Condition 1) is sufficient.

Condition 2)
Since \(|x| ≥ 0, |y| ≥ 0\) and \(3|x| + 2|y| = 0\), we have \(x = y = 0.\)
Therefore, \(3x + 4y = 0\). Condition 2) is sufficient.

FYI: Tip 1) of the VA method states that D is most likely to be the answer if conditions 1) and 2) provide the same information.

Therefore, the answer is D.
Answer: D
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 10 Feb 2019, 17:09
MathRevolution wrote:
[GMAT math practice question]

(function) Does \(f(x)=ax^4+bx^3+cx^2+dx+e\) have (\(x-2\)) as a factor?

\(1) f(2)=0\)
\(2) f(-2)=0\)


=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.
The statement that \(f(x)=ax^4+bx^3+cx^2+dx+e\) has \((x-2)\) as a factor is equivalent to saying \(f(x) = (x-2)g(x)\) for some function \(g(x)\). This is equivalent to the requirement that \(f(2) = 0\).

Thus condition 1) is sufficient.

Condition 2)
If \(f(x) = (x-2)(x+2)(x-1)(x+1)\), then \(f(x)\) has \(x-2\) as a factor, The answer is ‘yes’.
If \(f(x) = x(x+2)(x+1)(x-1)\), then \(f(x)\) doesn’t have \(x-2\) as a factor. The answer is ‘no’.
Since condition 2) does not yield a unique answer, condition 2) is not sufficient.

Therefore, the answer is A.
Answer: A
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 11 Feb 2019, 01:28
[GMAT math practice question]

(geometry) What is the area of a right triangle?

1) The length of one side is \(3\)
2) The length of one side is \(4\)
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 11 Feb 2019, 23:54
[GMAT math practice question]

(inequality) Is \(3(a-b)>0\)?

\(1) a^3>b^3\)
\(2) a>b\)
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 13 Feb 2019, 00:49
MathRevolution wrote:
[GMAT math practice question]

(geometry) What is the area of a right triangle?

1) The length of one side is \(3\)
2) The length of one side is \(4\)


=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

Since questions about triangles involve three variables, E is most likely to be the answer.

Conditions 1) & 2)
If the sides given are legs, then the area of the right triangle is \((\frac{1}{2})*3*4 = 6.\)
If one leg has length \(3\) and the hypotenuse has length \(4\), then, by Pythagoras’ theorem, the length of the other leg is \(\sqrt{(4^2 – 3^2)} = √7\), and the area of the triangle is \((\frac{1}{2})*3*√7 =\frac{(3√7)}{2}.\)
Thus, both conditions together are not sufficient, since they do not yield a unique solution.

Therefore, E is the answer.
Answer: E

In cases where 3 or more additional equations are required, such as for original conditions with “3 variables”, or “4 variables and 1 equation”, or “5 variables and 2 equations”, conditions 1) and 2) usually supply only one additional equation. Therefore, there is an 80% chance that E is the answer, a 15% chance that C is the answer, and a 5% chance that the answer is A, B or D. Since E (i.e. conditions 1) & 2) are NOT sufficient, when taken together) is most likely to be the answer, it is generally most efficient to begin by checking the sufficiency of conditions 1) and 2), when taken together. Obviously, there may be occasions on which the answer is A, B, C or D.
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 13 Feb 2019, 00:52
[GMAT math practice question]

(algebra) \(x^3-y^3=?\)

\(1) x-y=0\)
\(2) |x|=|y|\)
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 14 Feb 2019, 00:58
MathRevolution wrote:
[GMAT math practice question]

(inequality) Is \(3(a-b)>0\)?

\(1) a^3>b^3\)
\(2) a>b\)


=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

Asking if \(3(a-b)>0\) is equivalent to asking if \(a – b > 0\), or, equivalently, if \(a > b.\)
Thus, condition 2) is sufficient.

Condition 1)
\(a^3>b^3\)
\(=> a^3-b^3 > 0\)
\(=> (a-b)(a^2+ab+b^2) > 0\)
\(=> a - b > 0\) since \(a^2+ab+b^2 > 0\)
\(=> a > b\)
Thus, condition 1) is sufficient too.

Therefore, D is the answer.
Answer: D

FYI, Tip 1) of the VA method states that D is most likely to be the answer if conditions 1) and 2) provide the same information.
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 14 Feb 2019, 01:00
[GMAT math practice question]

(absolute value) Is \(|a|<1\)?

\(1) a^2<1\)
\(2) \frac{1}{(1-a^2)}>0\)
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6949
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS  [#permalink]

Show Tags

New post 15 Feb 2019, 00:18
MathRevolution wrote:
[GMAT math practice question]

(algebra) \(x^3-y^3=?\)

\(1) x-y=0\)
\(2) |x|=|y|\)


=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

\(x^3-y^3 = (x-y)(x^2+xy+y^2)\)

Condition 1)
If \(x – y = 0\), then \(x^3-y^3 = (x-y)(x^2+xy+y^2) = 0.\)
Thus, condition 1) is sufficient.

Condition 2)
If \(x = 1\) and \(y = 1\), then \(x^3-y^3 = 1 – 1 = 0.\)
If \(x = 1\) and \(y = -1\), then \(x^3-y^3 = 1 –(-1) = 2.\)
Condition 2) is not sufficient since it does not yield a unique solution.

Therefore, A is the answer.
Answer: A
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

GMAT Club Bot
Re: Math Revolution DS Expert - Ask Me Anything about GMAT DS   [#permalink] 15 Feb 2019, 00:18

Go to page   Previous    1   2   3   4   5   6   7   8   9   10   11   12   13    Next  [ 241 posts ] 

Display posts from previous: Sort by

Math Revolution DS Expert - Ask Me Anything about GMAT DS

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.