gmat prep

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sneakpeek: Newbie | Next Rank: 10 Posts; Posts: 8; Joined: Sun Jun 03, 2007 10:59 pm

by sneakpeek » Sun Jun 24, 2007 9:08 pm

Each of the numbers w,x,y, and z is equal to either 0 or 1. What is the value of w+x+y+z?

(1) w/2 + x/4 + y/8 + z/16 = 11/16
(2) w/3 + x/9 + y/27 + z/81 = 31/81

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Source: Beat The GMAT — Data Sufficiency | Sun Jun 24, 2007 9:08 pm

jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

Re: gmat prep

by jayhawk2001 » Sun Jun 24, 2007 9:30 pm

sneakpeek wrote:Each of the numbers w,x,y, and z is equal to either 0 or 1. What is the value of w+x+y+z?

(1) w/2 + x/4 + y/8 + z/16 = 11/16
(2) w/3 + x/9 + y/27 + z/81 = 31/81

1 - Sufficient.
Take the LCM and sum up the numerator
(8w + 4x + 2y + z) / 16
Since w, x, y and z are either 0 or 1, only possible combination
is w=1, x=0, y=1, z=1

2 - Sufficient.
(27w + 9x + 3y + z) / 81
Only w=1, x=0, y=1 and z=1 satisfy the above condition

Is it D ?

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sneakpeek: Newbie | Next Rank: 10 Posts; Posts: 8; Joined: Sun Jun 03, 2007 10:59 pm

by sneakpeek » Mon Jun 25, 2007 8:31 am

Yes, it is D. Thanks for your response!
Did you just plug in either 0 or 1 to the equation? Is that all I need to do?

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