GPREP (Properties of Numbers)

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zagcollins: Master | Next Rank: 500 Posts; Posts: 167; Joined: Wed Jun 11, 2008 10:58 pmFollowed by: 1 member; Thanked: 2 times

by zagcollins » Mon Jul 28, 2008 2:47 am

If xy+z=x(y+z), which of the following must be true?

A.x=0,z=0,
B.x=1,z=1
C.y=1 and z=0
D.x=1 or y=0
E.x=1 or z=0

OA Is E...

Last edited by zagcollins on Mon Jul 28, 2008 6:13 am, edited 1 time in total.

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Source: Beat The GMAT — Problem Solving | Mon Jul 28, 2008 2:47 am

sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

by sudhir3127 » Mon Jul 28, 2008 2:55 am

IMO A

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warlock: Senior | Next Rank: 100 Posts; Posts: 45; Joined: Tue Jul 22, 2008 7:24 pm; Thanked: 2 times

by warlock » Mon Jul 28, 2008 3:02 am

xy+z = x(y+z)

xy+z = xy+xz

z = xz

z-xz = 0

z(1-x) = 0

this means z=0 or (1-x) = 0

meaning z = 0 or x = 1.

so i guess the ans is option E.

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ricky: Master | Next Rank: 500 Posts; Posts: 118; Joined: Sun Jun 01, 2008 1:47 pmFollowed by: 1 member; Thanked: 5 times

by ricky » Mon Jul 28, 2008 3:04 am

IMO E..What is OA?

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parallel_chase: Legendary Member; Posts: 1153; Joined: Wed Jun 20, 2007 6:21 amFollowed by: 2 members; Thanked: 146 times

by parallel_chase » Mon Jul 28, 2008 3:08 am

E absolutely. Whats the OA?

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sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

by sudhir3127 » Mon Jul 28, 2008 3:21 am

Do we need to solve the eauation and find the values of X, y, z or the question mean for what values of X, y , Z the equation will be always true..

I understood it as the later one.. hence i opted for Zero, bcoz if its ) the LHS = RHS.. and will always hold true...

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parallel_chase: Legendary Member; Posts: 1153; Joined: Wed Jun 20, 2007 6:21 amFollowed by: 2 members; Thanked: 146 times

by parallel_chase » Mon Jul 28, 2008 3:29 am

sudhir3127 wrote:Do we need to solve the eauation and find the values of X, y, z or the question mean for what values of X, y , Z the equation will be always true..

I understood it as the later one.. hence i opted for Zero, bcoz if its ) the LHS = RHS.. and will always hold true...

Well if you go by that way even the second option would hold true, x=1,z=1

xy+z=x(y+z)

y+1=y+1

On GMAT you cannot have 2 right answers, therefore option E is the correct.

I hope its clear.

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