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# If xy = -6, what is the value of xy(x+y)?

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If xy = -6, what is the value of xy(x+y)?  [#permalink]

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22 Feb 2020, 21:02
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Difficulty:

45% (medium)

Question Stats:

53% (01:20) correct 47% (01:28) wrong based on 15 sessions

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If xy = -6, what is the value of xy(x+y)?

(1) x - y = 5

(2) xy^2 = 18

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If xy = -6, what is the value of xy(x+y)?  [#permalink]

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22 Feb 2020, 21:42
If xy = -6, what is the value of xy(x+y)?

(1) x - y = 5
So xy=-6 and x-y=5 or x=y+5, but we can have different values..
$$xy=-6....(y+5)y=-6....y^2+5y+6=0......y^2+2y+3y+6=0....(y+2)(y+3)=0$$
So y can be -2, hence x=3 and $$xy(x+y)=-6(3-2)=-6$$
y can be -3, hence x=2 and $$xy(x+y)=-6(2-3)=6$$
Insuff

(2) $$xy^2 = 18...xy*y=18....-6*y=18...y=-3$$
hence x=2 and $$xy(x+y)=-6(2-3)=6$$
Suff

B
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Re: If xy = -6, what is the value of xy(x+y)?  [#permalink]

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22 Feb 2020, 21:44
1. (x-y)^2= (x+y)^2 -4xy
(X+y)^2= 25+4xy = 25-4*-6 = 25-24=1
X+y =1 or x+y = -1
Not sufficient

2. Xy^2=18
Xy*y=18
-6*y=18
Y=-3
X=2
X+y=-1
Sufficient
Ans B

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If xy = -6, what is the value of xy(x+y)?  [#permalink]

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22 Feb 2020, 22:37
Quote:
If xy = -6, what is the value of xy(x+y)?

(1) x - y = 5

(2) xy^2 = 18

HI chetan2u, VeritasKarishma, Bunuel, GMATBusters, GMATPrepNow, EgmatQuantExpert, GMATinsight , GMATGuruNY, MentorTutoring

Is it not advisable to use the numbers in these kinds of problems?

If xy = -6 there multiple possibilities with integers 6,1 & 2,3 with sign changes.Little but confused using algebra into the questions.

Below is the link to the Gmatclub test question.

https://gmatclub.com/forum/d01-183504.html
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If xy = -6, what is the value of xy(x+y)?  [#permalink]

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22 Feb 2020, 23:20
It depends on how quick you are at numbers picking.

for xy = - 6, we can have (x,y) can be (-1,6) , (6,-1), (3,-2), (2,-3)... and many other values
but (3,-2), (2,-3) satisfy St 1 : x-y = 5

and (3,-2), (2,-3) gives 2 different answer for xy(x+y)

So, St1 is not sufficient.

Thus Number picking seems a bit more difficult.

Also, I would recommend practicing more Algebra, because Algebra is unavoidable and will be used for other questions also.

NandishSS wrote:
Quote:
If xy = -6, what is the value of xy(x+y)?

(1) x - y = 5

(2) xy^2 = 18

HI chetan2u, VeritasKarishma, Bunuel, GMATBusters, GMATPrepNow, EgmatQuantExpert, GMATinsight , GMATGuruNY, MentorTutoring

Is it not advisable to use the numbers in these kinds of problems?

If xy = -6 there multiple possibilities with integers 6,1 & 2,3 with sign changes.Little but confused using algebra into the questions.

Below is the link to the Gmatclub test question.

https://gmatclub.com/forum/d01-183504.html

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Re: If xy = -6, what is the value of xy(x+y)?  [#permalink]

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22 Feb 2020, 23:51
HI RashedVai

This question is discussed in the below link.

Bunuel FYI

https://gmatclub.com/forum/if-xy-6-what ... 67646.html
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Re: If xy = -6, what is the value of xy(x+y)?  [#permalink]

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22 Feb 2020, 23:54
GMATBusters wrote:
It depends on how quick you are at numbers picking.

for xy = - 6, we can have (x,y) can be (-1,6) , (6,-1), (3,-2), (2,-3)... and many other values
but (3,-2), (2,-3) satisfy St 1 : x-y = 5

and (3,-2), (2,-3) gives 2 different answer for xy(x+y)

So, St1 is not sufficient.

Thus Number picking seems a bit more difficult.

Also, I would recommend practicing more Algebra, because Algebra is unavoidable and will be used for other questions also.

NandishSS wrote:
Quote:
If xy = -6, what is the value of xy(x+y)?

(1) x - y = 5

(2) xy^2 = 18

HI chetan2u, VeritasKarishma, Bunuel, GMATBusters, GMATPrepNow, EgmatQuantExpert, GMATinsight , GMATGuruNY, MentorTutoring

Is it not advisable to use the numbers in these kinds of problems?

If xy = -6 there multiple possibilities with integers 6,1 & 2,3 with sign changes.Little but confused using algebra into the questions.

Below is the link to the Gmatclub test question.

https://gmatclub.com/forum/d01-183504.html

Thank you GMATBusters , Will practice using Algebra as well
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Re: If xy = -6, what is the value of xy(x+y)?  [#permalink]

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23 Feb 2020, 02:43
RashedVai wrote:
If xy = -6, what is the value of xy(x+y)?

(1) x - y = 5

(2) xy^2 = 18

Discussed here: https://gmatclub.com/forum/if-xy-6-what ... 67646.html Hope it helps.

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Re: If xy = -6, what is the value of xy(x+y)?   [#permalink] 23 Feb 2020, 02:43
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