Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1 : GMAT Data Sufficiency (DS)
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# Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1

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Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1 [#permalink]

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24 Nov 2009, 20:56
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Is xy > x^2*y^2?

(1) 14*x^2 = 3
(2) y^2 = 1
[Reveal] Spoiler: OA

Last edited by Bunuel on 16 Feb 2012, 21:37, edited 1 time in total.
Edited the question and added the OA
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24 Nov 2009, 21:33
E

both statements dont reference both X and Y

and statement 2 leaves Y with both positive and negative values thus it can be greater or less. (also the square of X is less than X but that doesnt matter if the products can be positive or negative)
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26 Nov 2009, 00:21
Let's consider both statements together

$$xy$$ could be positive or negative;

if $$xy<0$$, clearly $$xy \leq x^2y^2$$, no calculations are needed. Inequality in question stem is false

If $$xy>0$$, than $$y=1; x=sqrt{3/14}$$ or $$y=-1; x=-sqrt{3/14}$$. once more no need to calculate this, just note that $$xy<1$$. In this case $$(xy)^2<xy<1$$

[strike]So, in both cases $$xy<x^2y^2$$[/strike]

Last edited by shalva on 27 Nov 2009, 04:10, edited 1 time in total.
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26 Nov 2009, 19:43
shalva wrote:
Let's consider both statements together

$$xy$$ could be positive or negative;

if $$xy<0$$, clearly $$xy \leq x^2y^2$$, no calculations are needed. Inequality in question stem is false

If $$xy>0$$, than $$y=1; x=sqrt{3/14}$$ or $$y=-1; x=-sqrt{3/14}$$. once more no need to calculate this, just note that $$xy<1$$. In this case (xy)^2<xy<1

So, in both cases xy<x^2y^2

(C)

I don't get this, in the blue part, you mentioned that (xy)^2<xy, then your conclusion (the red part) was in both cases xy<x^2y^2.

Anyway, IMO, E is the answer because (xy)^2 = 3/14.
If xy<0, clearly that xy<(xy)^2.
If xy>0, because (xy)^2 =3/14 <1 => xy>(xy)^2.

Hence E.
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27 Nov 2009, 04:11
fall2009 wrote:
I don't get this, in the blue part, you mentioned that (xy)^2<xy, then your conclusion (the red part) was in both cases xy<x^2y^2.

Anyway, IMO, E is the answer because (xy)^2 = 3/14.
If xy<0, clearly that xy<(xy)^2.
If xy>0, because (xy)^2 =3/14 <1 => xy>(xy)^2.

Hence E.

You're absolutely right In one case $$xy<x^2y^2$$, in other - $$xy>x^2y^2$$
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Re: Is xy > x2y2? (1) 14x2 = 3 (2) y2 = 1 [#permalink]

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16 Feb 2012, 19:42
if as follows:
xy - x^2*y^2 > 0
xy(1- xy) > 0
so, xy>0
or, x>0 or, y>0
and 1-xy > 0
xy<1
Thus no statements are sufficient.
Ans. E

What are wrongs with this approach?
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Re: Is xy > x2y2? (1) 14x2 = 3 (2) y2 = 1 [#permalink]

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16 Feb 2012, 21:44
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Baten80 wrote:
if as follows:
xy - x^2*y^2 > 0
xy(1- xy) > 0
so, xy>0
or, x>0 or, y>0
and 1-xy > 0
xy<1
Thus no statements are sufficient.
Ans. E

What are wrongs with this approach?

Is xy > x^2*y^2?

Is $$xy>x^2*y^2$$? --> is $$0<xy<1$$? (the same way as a>a^2 means 0<a<1)

(1) 14*x^2 = 3. Clearly insufficient, since no info about y.
(2) y^2 = 1. Clearly insufficient, since no info about x.

(1)+(2) If $$x$$ and $$y$$ have the same sign then $$xy=\sqrt{\frac{3}{14}}$$ and the answer will be YES but if $$x$$ and $$y$$ have the opposite signs then $$xy=-\sqrt{\frac{3}{14}}$$ and the answer will be NO. Not sufficient.

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Re: Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1 [#permalink]

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23 Feb 2014, 05:02
Bumping for review and further discussion.
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Re: Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1 [#permalink]

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10 Mar 2015, 08:13
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1 [#permalink]

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29 Apr 2015, 22:46
Bunuel wrote:
Baten80 wrote:
if as follows:
xy - x^2*y^2 > 0
xy(1- xy) > 0
so, xy>0
or, x>0 or, y>0
and 1-xy > 0
xy<1
Thus no statements are sufficient.
Ans. E

What are wrongs with this approach?

Is xy > x^2*y^2?

Is $$xy>x^2*y^2$$? --> is $$0<xy<1$$? (the same way as a>a^2 means 0<a<1)

(1) 14*x^2 = 3. Clearly insufficient, since no info about y.
(2) y^2 = 1. Clearly insufficient, since no info about x.

(1)+(2) If $$x$$ and $$y$$ have the same sign then $$xy=\sqrt{\frac{3}{14}}$$ and the answer will be YES but if $$x$$ and $$y$$ have the opposite signs then $$xy=-\sqrt{\frac{3}{14}}$$ and the answer will be NO. Not sufficient.

Hi Bunuel,

Can you explain how you got this step? Thanks!

Is xy>x2∗y2? --> is 0<xy<1? (the same way as a>a^2 means 0<a<1)
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Re: Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1 [#permalink]

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30 Apr 2015, 02:30
amnesia604 wrote:
Bunuel wrote:
Baten80 wrote:
if as follows:
xy - x^2*y^2 > 0
xy(1- xy) > 0
so, xy>0
or, x>0 or, y>0
and 1-xy > 0
xy<1
Thus no statements are sufficient.
Ans. E

What are wrongs with this approach?

Is xy > x^2*y^2?

Is $$xy>x^2*y^2$$? --> is $$0<xy<1$$? (the same way as a>a^2 means 0<a<1)

(1) 14*x^2 = 3. Clearly insufficient, since no info about y.
(2) y^2 = 1. Clearly insufficient, since no info about x.

(1)+(2) If $$x$$ and $$y$$ have the same sign then $$xy=\sqrt{\frac{3}{14}}$$ and the answer will be YES but if $$x$$ and $$y$$ have the opposite signs then $$xy=-\sqrt{\frac{3}{14}}$$ and the answer will be NO. Not sufficient.

Hi Bunuel,

Can you explain how you got this step? Thanks!

Is xy>x2∗y2? --> is 0<xy<1? (the same way as a>a^2 means 0<a<1)

$$xy>x^2*y^2$$;
$$xy>(xy)^2$$;
$$xy(1-xy)>0$$;
$$0<xy<1$$.

Hope it helps.
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Re: Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1 [#permalink]

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13 Mar 2016, 07:34
Here nothing is specified about the values of x adn y being >0 or <0
so => not sufficient.
hence E
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06 Jun 2016, 12:52
Is xy>(x^2)(y^2)

1) 14x^2=3

2) y^2=1
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06 Jun 2016, 14:26
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pepo wrote:
Is xy>(x^2)(y^2)

1) 14x^2=3

2) y^2=1

Dear pepo,

Please don't begin new threads for math questions that are already discussed here on GMAT Club. This particular question is already posted here:
is-xy-x-2-y-2-1-14-x-2-3-2-y-87269.html
I will ask Bunuel to merge the two posts.

You can find a detailed discussion at that link, and if you still have a question, that would be the appropriate place to ask it, once these posts are merged.

Does all this make sense?
Mike
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Re: Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1 [#permalink]

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06 Jun 2016, 22:54
pepo wrote:
Is xy>(x^2)(y^2)

1) 14x^2=3

2) y^2=1

Merging topics. Please refer to the discussion above.
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Re: Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1 [#permalink]

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06 Jun 2016, 23:18
mikemcgarry wrote:
pepo wrote:
Is xy>(x^2)(y^2)

1) 14x^2=3

2) y^2=1

Dear pepo,

Please don't begin new threads for math questions that are already discussed here on GMAT Club. This particular question is already posted here:
is-xy-x-2-y-2-1-14-x-2-3-2-y-87269.html
I will ask Bunuel to merge the two posts.

You can find a detailed discussion at that link, and if you still have a question, that would be the appropriate place to ask it, once these posts are merged.

Does all this make sense?
Mike

Ok thanks and sorry for the unconvenient
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Re: Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1 [#permalink]

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06 Jun 2016, 23:41
Is xy > x^2*y^2?

(1) 14*x^2 = 3
(2) y^2 = 1

xy > $$x^2$$*$$y^2$$

xy - $$x^2$$*$$y^2$$ > 0

xy (1-xy) > 0

0<xy < 1 --> This is our revised problem

Statement 1 --> clearly not sufficient, as no info about y.

Statement 2 --> clearly not sufficient, as no info about y.

Combining (1) and (2)

$$x^2$$*$$y^2$$ = 3/14.

One of the solution of xy lies between 0 and 1;

Other solution does not lie between 0 and 1 .

So not sufficient.

Re: Is xy > x^2*y^2? (1) 14*x^2 = 3 (2) y^2 = 1   [#permalink] 06 Jun 2016, 23:41
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