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# xy > 0

Author Message
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GMAT Club Legend
Joined: 07 Jun 2014
Posts: 4749
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 93

Kudos [?]: 1651 [0], given: 396

xy > 0 [#permalink]  23 Jun 2018, 12:08
Expert's post
00:00

Question Stats:

96% (00:47) correct 3% (00:55) wrong based on 26 sessions
$$xy > 0$$
 Quantity A Quantity B $$(2x - y)(x + 4y)$$ $$2x^2$$ + $$8xy$$ – $$4y^2$$

A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.
[Reveal] Spoiler: OA

_________________

Sandy
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Director
Joined: 20 Apr 2016
Posts: 756
Followers: 6

Kudos [?]: 511 [0], given: 94

Re: xy > 0 [#permalink]  29 Jun 2018, 05:22
sandy wrote:
$$xy > 0$$
 Quantity A Quantity B $$(2x - y)(x + 4y)$$ $$2x^2$$ + $$8xy$$ – $$4y^2$$

A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.

Here;
Statement 1: $$(2x - y)(x + 4y)$$ = $$2x^2$$+ $$8xy$$ - $$xy$$– $$4y^2$$ = $$2x^2$$ + $$7xy$$ –$$4y^2$$

Statement 2:$$2x^2$$+ $$8xy$$ – $$4y^2$$
Since xy>0

Therefore Statement 1 < Statement 2
_________________

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GMAT Club Legend
Joined: 07 Jun 2014
Posts: 4749
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 93

Kudos [?]: 1651 [0], given: 396

Re: xy > 0 [#permalink]  16 Jul 2018, 18:54
Expert's post
Explanation

the terms in Quantity A:
$$(2x - y)(x + 4y) = 2x^2 + 8xy - xy - 4y^2 = 2x^2 + 7xy - 4y2$$

Since $$2x^2$$ and $$-4y^2$$ appear in both quantities, eliminate them.

Quantity A is now equal to 7xy and Quantity B is now equal to 8xy.

Because xy > 0, Quantity B is greater. (Don’t assume! If xy were zero, the two quantities would have been equal. If xy were negative, Quantity A would have been greater.)
_________________

Sandy
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Re: xy > 0   [#permalink] 16 Jul 2018, 18:54
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