Author 
Message 
Intern
Joined: 25 Sep 2008
Posts: 6

3
This post received KUDOS
3
This post was BOOKMARKED
If \(x\) is a positive integer, is \(y^2(x^3x+1)>75?\) (1) \(y>1\) (2) \((x1)^2=16\) Source: GMAT Club Tests  hardest GMAT questions Hi,
I think the answer/ explanation of this question is wrong.
Here is the official explanation:  We need to know two things here
The value of x Whether y is greater than 1 From S1, we only know that y>1
From S2, we only have the value of x. we also know that x is positive. So, we have to only consider the positive root. Combining the two statements, we have the required information. The correct answer is C.  However, i think the answer is E, since we dont have any information on whether y is an integer or not. It can be possible that y is a fraction. Am i missing something guys????



SVP
Joined: 30 Apr 2008
Posts: 1874
Location: Oklahoma City
Schools: Hard Knocks

Re: m02 #21 [#permalink]
Show Tags
14 Nov 2008, 14:27
When you consider the statements together, you must use Statement 1 which tells you that 1 is greater than 1. It could be a fraction, but it will be a fraction greater than 1, thus making the statements together, still sufficient. jimmiejaz wrote: Hi,
I think the answer/ explanation of this question is wrong.
If x is a positive integer, is y^2(x^3x+1)>75? 1. y>1 2. (x1)^2=16
Here is the official explanation:  We need to know two things here
The value of y Whether y is greater than 1 From S1, we only know that y>1
From S2, we only have the value of x. we also know that x is positive. So, we have to only consider the positive root. Combining the two statements, we have the required information. The correct answer is C.  However, i think the answer is E, since we dont have any information on whether y is an integer or not. It can be possible that y is a fraction. Am i missing something guys????
_________________
 J Allen Morris **I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.
GMAT Club Premium Membership  big benefits and savings



CIO
Joined: 02 Oct 2007
Posts: 1218

Re: m02 #21 [#permalink]
Show Tags
27 Nov 2008, 08:28
Hi. From S2 we know that x=5. If x=5 we know that (x^3x+1)=1255+1=121. As long as y>1, we are sure that y^2(x^3x+1)>75. Hope this makes sense. jimmiejaz wrote: Hi,
I think the answer/ explanation of this question is wrong.
If x is a positive integer, is y^2(x^3x+1)>75? 1. y>1 2. (x1)^2=16
Here is the official explanation:  We need to know two things here
The value of x Whether y is greater than 1 From S1, we only know that y>1
From S2, we only have the value of x. we also know that x is positive. So, we have to only consider the positive root. Combining the two statements, we have the required information. The correct answer is C.  However, i think the answer is E, since we dont have any information on whether y is an integer or not. It can be possible that y is a fraction. Am i missing something guys????
_________________
Welcome to GMAT Club! Want to solve GMAT questions on the go? GMAT Club iPhone app will help. Please read this before posting in GMAT Club Tests forum 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



SVP
Joined: 29 Aug 2007
Posts: 2473

Re: m02 #21 [#permalink]
Show Tags
27 Nov 2008, 09:14
jimmiejaz wrote: Hi,
I think the answer/ explanation of this question is wrong.
If x is a positive integer, is y^2(x^3x+1)>75? 1. y>1 2. (x1)^2=16
Here is the official explanation:  We need to know two things here
The value of x Whether y is greater than 1 From S1, we only know that y>1
From S2, we only have the value of x. we also know that x is positive. So, we have to only consider the positive root. Combining the two statements, we have the required information. The correct answer is C.  However, i think the answer is E, since we dont have any information on whether y is an integer or not. It can be possible that y is a fraction. Am i missing something guys???? Both statement togather are suff. we need two things i.e. values of x and y. Statement 1 tells us the range of y. Statement 2 tells us the value of x. so togather the value of y^2 (x^3  x + 1) is at least > 121. suff. C.
_________________
Verbal: http://gmatclub.com/forum/newtotheverbalforumpleasereadthisfirst77546.html Math: http://gmatclub.com/forum/newtothemathforumpleasereadthisfirst77764.html Gmat: http://gmatclub.com/forum/everythingyouneedtoprepareforthegmatrevised77983.html
GT



Manager
Joined: 02 Aug 2007
Posts: 228
Schools: Life

Re: m02 #21 [#permalink]
Show Tags
10 Jan 2009, 20:40
1
This post received KUDOS
In statement 2 why don't we account for: x1 = 4 ==> x = 3 and x1 = 4 ==> x = 5 This would yield E as the answer. Am I missing something?



CIO
Joined: 02 Oct 2007
Posts: 1218

Re: m02 #21 [#permalink]
Show Tags
12 Jan 2009, 04:12
2
This post received KUDOS
We know from the question stem that \(x\) is a positive integer. xALIx wrote: In statement 2 why don't we account for: x1 = 4 ==> x = 3 and x1 = 4 ==> x = 5 This would yield E as the answer. Am I missing something?
_________________
Welcome to GMAT Club! Want to solve GMAT questions on the go? GMAT Club iPhone app will help. Please read this before posting in GMAT Club Tests forum 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



Founder
Joined: 04 Dec 2002
Posts: 15153
Location: United States (WA)

Re: m02 #21 [#permalink]
Show Tags
28 Feb 2009, 22:57
Just a useful reminder  you can write mathematical expressions in the posts by enclosing them in the [m] math [/m] tags. If you don't want to write those out, just select the line or part of the text that you want to be converted into math, and hit the "m" button in the menu (the one directly below the big "B") and the software will automatically insert the tags. You can also include a reference to the test question by hitting the "t" button.
_________________
Founder of GMAT Club
US News Rankings progression  last 10 years in a snapshot  New! Just starting out with GMAT? Start here... Need GMAT Book Recommendations? Best GMAT Books
Coauthor of the GMAT Club tests



Intern
Joined: 03 Apr 2010
Posts: 29

Re: m02 #21 [#permalink]
Show Tags
30 Apr 2010, 06:17
by expanding \((x1)^2=16\) using foil, I created a quadratic equation \(x^22x15=0\) This produced the expression \((x5)*(x+3)=0\) .... Plugging the solutions x=5 and x=3 into the question stem I produced a "maybe" or "yes and no" answer to the question stem and rendered an answer of E! Please help!



CIO
Joined: 02 Oct 2007
Posts: 1218

Re: m02 #21 [#permalink]
Show Tags
11 May 2010, 02:48
1
This post received KUDOS
You forget that \(x\) is a positive integer, as stated in the question stem. jbark55 wrote: by expanding \((x1)^2=16\) using foil, I created a quadratic equation \(x^22x15=0\) This produced the expression \((x5)*(x+3)=0\) .... Plugging the solutions x=5 and x=3 into the question stem I produced a "maybe" or "yes and no" answer to the question stem and rendered an answer of E! Please help!
_________________
Welcome to GMAT Club! Want to solve GMAT questions on the go? GMAT Club iPhone app will help. Please read this before posting in GMAT Club Tests forum 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: 09 Mar 2010
Posts: 3

Re: m02 #21 [#permalink]
Show Tags
11 May 2010, 08:20
2
This post received KUDOS
My answer is C. This probem is similar to one given in the OG.
If x is a positive integer, is y^2(x^3x+1)>75? 1. y>1 2. (x1)^2=16
1. Insufficient. Y can be any number >1 and no X value is given. 2. Insufficient however statement 2 does give good information
(x1)^2=16 can be simplified to read:
take the sqrt of both sides. x1 = 4
x = 5... however we dont know what x is.
so we take statement 1 and combine with statement 2 and we can solve the equation.



Manager
Affiliations: NCC,SAE,YHIA
Joined: 04 May 2010
Posts: 51
Location: Mumbai , India
WE 1: 3 years international sales & mktgprojects

Re: m02 #21 [#permalink]
Show Tags
11 May 2010, 08:44
1
This post received KUDOS
1
This post was BOOKMARKED
\((x1)^2 = 16\) shall be simplified as \(x1=+4\) or \(x=+5\), \(x=3\) if we consider \((x1)^2=4^2\) and consider \(x1 = 4\) We miss the second root ie \(x =3\)<quadratic equation must have 2 roots>. In this question we are spared even if we consider \(x1=4\) , However if question had not specified x as positive integer, answer would have been E. \(y^2(x^3x+1)\) +ve in case \(x=+5\) and ve in case \(x=3\). Good question...
_________________
Sun TzuVictorious warriors win first and then go to war, while defeated warriors go to war first and then seek to win.



Manager
Joined: 16 Apr 2008
Posts: 90

Re: m02 #21 [#permalink]
Show Tags
11 May 2010, 10:51
S1 is not sufficient as no info about x S2 is not sufficient as no info about y
S2implies x=5, so as long as S1 is true (i.e. y>1) the inequality in the stem is holds good.
So Answer C



Director
Joined: 21 Dec 2009
Posts: 583
Concentration: Entrepreneurship, Finance

Re: m02 #21 [#permalink]
Show Tags
11 May 2010, 14:04
we already know statement (1) or (2) proved insufficient when considered individually. When Combined, we get y^2(121) since y>1, the expression becomes (1 + k)(121)....k is some positive value being part of y. That is: 121 + 121k > 75 correct response is C
_________________
KUDOS me if you feel my contribution has helped you.



Intern
Joined: 29 Mar 2010
Posts: 16
Schools: UCLA, USC
WE 1: 3 Yr at leading SAAS company

Re: m02 #21 [#permalink]
Show Tags
11 May 2010, 15:52
If x is a positive integer, is y^2(x^3x+1)>75
1. y>1 2. (x1)^2=16
St 1 alone is not suff(B & D elimitated)
St2: =>x=5,3 (Since x is +ve , x=5) St 2 alone is not suff(A & D eliminated)
Now, Combining both y>1 & x=5
y^2(x^3x+1)>75 => OA is C.



Manager
Joined: 15 Sep 2009
Posts: 134

Re: m02 #21 [#permalink]
Show Tags
11 May 2010, 23:43
First I took statement 2 , We get x = 5 since x =3 is ruled out. Applying x = 5 in the eqn we get y (121) > 75.For this expr to be true I want atleast y > 1 which is in statment 1. So each statement alone is insuff whereas both the statements combined can yield a result..
I will go with option C



Manager
Joined: 08 May 2010
Posts: 143

Re: m02 #21 [#permalink]
Show Tags
20 May 2010, 05:55
So immediately we are told more about x than y. We know that x is a positive integer. This being so, the whole blob of Xcubed whatever can be nothing less than 1. X cannot be less than 1 and so xcubed minus x plus 1 can be nothing less than 1. Now we need to know more about y.
Statement 1. tells us that y is greater than 1. This coupled with what we know about x is insufficient to tell us if the whole thing is greater than 75. Statement 1 did not tell us anything more than what we knew about x (that it is equal to or greater than 1), and not enough about y. Not sufficient.
Statement 2. (x1)squared =16. This still tells us nothing about y and thus will likely be insufficient by itself.
But lets look further. FOILing out the (X1)(x1) = x^2 2x+1=16 >X^2 2x15=0. Now factoring this we get (x+3)(x5)=0. So x could be either 3 or 5. We know that x cannot be negative from the initial statement. So x must be 5. Then plugging 5 back into the x cubed thing we get 1255+1=121. So (y^2)121. Y is greater than 1 so the product must be greater than 75. If we put statements 1 and 2 together we get C. 1 and 2 are sufficient together.
If these comments were helpful, please give kudos. Thanks, Skip



Manager
Joined: 08 May 2010
Posts: 143

Re: m02 #21 [#permalink]
Show Tags
20 May 2010, 05:58
Something important that occurs to me about this question. To go through that whole process may take to long to be SURE of what the answer is. If you can do this math quickly and under two minutes okay. At some point it may be better to get this ? wrong than to waste a huge amt of time on it.



SVP
Joined: 16 Nov 2010
Posts: 1663
Location: United States (IN)
Concentration: Strategy, Technology

Re: m02 #21 [#permalink]
Show Tags
13 May 2011, 04:34
(1) is insufficient y = 2 x = 1 4 * 1 < 75 y = 77 x = 1 (77)^2 * 1 > 75 (2) x = 4 + 1 = 5 But no information about y, hence insufficient (1) + (2) y = 2, x = 5 4 * (125  5 + 1) = 484 > 75 So y will always increase, hence value will be always > 75. Answer  C
_________________
Formula of Life > Achievement/Potential = k * Happiness (where k is a constant)
GMAT Club Premium Membership  big benefits and savings



Manager
Joined: 15 Apr 2011
Posts: 64
Location: Bangalore India
Schools: LBS, HBS, ISB, Kelloggs, INSEAD

Re: m02 #21 [#permalink]
Show Tags
13 May 2011, 05:45
xALIx wrote: In statement 2 why don't we account for: x1 = 4 ==> x = 3 and x1 = 4 ==> x = 5 This would yield E as the answer. Am I missing something? The question clearly says that x is a positive integer than x1 can only be equal to 4 in that case.
_________________
Thanks, AM



Director
Joined: 01 Feb 2011
Posts: 755

Re: m02 #21 [#permalink]
Show Tags
13 May 2011, 06:15
1. Not sufficient as we don't know anything about x.
2. Not sufficient As we don't know anything about y.
Together Sufficient as y>1,x=5
Given expression>75
Answer is C.
Posted from my mobile device







Go to page
1 2
Next
[ 29 posts ]




