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What is the value of xy?

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Intern
Joined: 13 Oct 2011
Posts: 17
Followers: 0

Kudos [?]: 10 [0], given: 16

What is the value of xy? [#permalink]  05 Jan 2012, 18:09
00:00

Difficulty:

(N/A)

Question Stats:

88% (01:33) correct 13% (01:32) wrong based on 8 sessions
What is xy?

1) y=x+1
2) y=x^2+1
Answer is e, can someone explain why each statement is not sufficient?
[Reveal] Spoiler: OA
Manager
Status: Meh, I can't take the GMAT before 2017.
Joined: 20 Aug 2011
Posts: 146
Followers: 3

Kudos [?]: 72 [2] , given: 0

Re: What is the value of xy? [#permalink]  05 Jan 2012, 19:49
2
KUDOS
Question is- can you find the exact value of xy.

1.
y=x+1
there is no way to determine value of x or y.
x can be a fraction, positive/negative integer.

Insufficient.

2.
y=x^2+1
all we know that y is positive.
Insufficient.

1+2
x+1=x^2+1
x^2=x
x is 0 or 1
y is 1 or 2

xy=0 or 2.
Insufficient

Hence E
Intern
Joined: 13 Oct 2011
Posts: 17
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Kudos [?]: 10 [0], given: 16

Re: What is the value of xy? [#permalink]  05 Jan 2012, 20:03
thanks! excellent explanation! Kudos given!
Manager
Status: Meh, I can't take the GMAT before 2017.
Joined: 20 Aug 2011
Posts: 146
Followers: 3

Kudos [?]: 72 [0], given: 0

Re: What is the value of xy? [#permalink]  05 Jan 2012, 20:31
hi shawndx
No problem.. I'm happy to help people with their GMAT prep.
Manager
Joined: 29 Jul 2011
Posts: 108
Location: United States
Followers: 4

Kudos [?]: 44 [0], given: 6

Re: What is the value of xy? [#permalink]  06 Jan 2012, 17:57
1. y=x+1. multiply both sides by x -> xy=x(x+1). No info on x, insuff.
2. y=x^2+1. multiply both sides by x -> xy=x(x^2+1). No info on x, insuff.

Together, equating both statements -> x+1 = x^2+1 -> x = 0, 1
Substituting gives y = 1,2.

Two solutions for xy -> E.
_________________

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Please consider giving +1 Kudos if deserved!

DS - If negative answer only, still sufficient. No need to find exact solution.
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Intern
Joined: 07 Jan 2012
Posts: 7
Location: United States
WE: Marketing (Other)
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Kudos [?]: 6 [0], given: 0

Re: What is the value of xy? [#permalink]  07 Jan 2012, 02:15
Statement 1 and 2 considered individually are clearly insufficient. When we combine these two, we get two solutions as below:

x^2-x=0
x(x-1)=0
x=0 OR x=1

X=0, Y=1, XY = 0
X = 1, Y=2, XY = 2

Thus we have two solutions here and answer is E
Re: What is the value of xy?   [#permalink] 07 Jan 2012, 02:15
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