What is y? 1. y^3 + 2y = y + 2*y^2 2. y^2 = y : DS Archive
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# What is y? 1. y^3 + 2y = y + 2*y^2 2. y^2 = y

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What is y? 1. y^3 + 2y = y + 2*y^2 2. y^2 = y [#permalink]

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18 Oct 2007, 13:18
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What is y?

1. y^3 + 2y = y + 2*y^2
2. y^2 = y
CEO
Joined: 21 Jan 2007
Posts: 2756
Location: New York City
Followers: 11

Kudos [?]: 854 [0], given: 4

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18 Oct 2007, 13:19
bmwhype2 wrote:
What is y?

1. y^3 + 2y = y + 2*y^2
2. y^2 = y

1. Set up a quad equation. factor out y. therefore y=0. solve for the rest. y=1.

2. y can be 0 or 1.

Can we have two answers for a DS question?
Manager
Joined: 18 Jun 2007
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18 Oct 2007, 17:47
ah damn, forgot about the integer 0.

I think the answer is E. y is 0 or 1 for both.
GMAT Club Legend
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18 Oct 2007, 17:59
St1:
y^3 + y - 2y^2 = 0
y(y^2 -2y + 1) = 0
y(y-1)^2 = 0
y can be 0 or 1.
Insufficient.

St2:
y^2 - y = 0
y(y-1) = 0
y can be 0 or 1.
Insufficient.

St1 and St2:
Nothing new made known to us. Insufficient.

Ans E
Director
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18 Oct 2007, 19:15
ywilfred wrote:
St1:
y^3 + y - 2y^2 = 0
y(y^2 -2y + 1) = 0
y(y-1)^2 = 0
y can be 0 or 1.
Insufficient.

St2:
y^2 - y = 0
y(y-1) = 0
y can be 0 or 1.
Insufficient.

St1 and St2:
Nothing new made known to us. Insufficient.

Ans E

Agree E it is

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18 Oct 2007, 19:45
I get A...

y=?

(1)

y^3 + 2y=y+2y^2

y(y^2 +2)= y+2y^2

y^2+2=1+2y

y^2-2y+1

(y-1)(y-1) y=1

sufficient

2)

y can be 0 or 1
Director
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Kudos [?]: 50 [0], given: 0

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18 Oct 2007, 19:46
fresinha12 wrote:
I get A...

y=?

(1)

y^3 + 2y=y+2y^2

y(y^2 +2)= y+2y^2

y^2+2=1+2y

y^2-2y+1

(y-1)(y-1) y=1

sufficient

2)

y can be 0 or 1

1) y can be zero as well ..

and given y could be zero the simplification is also invallid...

I always get caught with !zero!
18 Oct 2007, 19:46
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