Another Absolute value question

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gmat009: Master | Next Rank: 500 Posts; Posts: 458; Joined: Sun Aug 31, 2008 10:44 amFollowed by: 1 member; Thanked: 3 times

by gmat009 » Thu Oct 09, 2008 11:01 am

Is |x| = y - z ?
(1) x + y = z
(2) x < 0

here is how how approached :-

To prove:- x=y-z
OR -x=y-z or x=z-y

a) x+y=z
or x=z-y {sufficient}

b) x<0 {insufficient}

Plz. let me know if I am wrong somewhere.....

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Source: Beat The GMAT — Data Sufficiency | Thu Oct 09, 2008 11:01 am

rtfact: Newbie | Next Rank: 10 Posts; Posts: 9; Joined: Tue Sep 16, 2008 9:44 am

by rtfact » Thu Oct 09, 2008 11:15 am

the answer is C since:

(1) x+y=z --> -x=y-z thus |x|=y-z is true only if x<=0.
for example, if x=1 then according to (1): -1=y-z which contradicts: 1=y-z
insufficient.

(2) x<0 insufficient as you said.

(1+2) sufficient. x<0, therefore in statement (1): -x=y-z, x is positive, which leads us to conclude that |x|=y-z is true.

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Gmatss: Senior | Next Rank: 100 Posts; Posts: 67; Joined: Tue Sep 16, 2008 9:29 pm; Location: new york; Thanked: 2 times

by Gmatss » Thu Oct 09, 2008 11:18 am

is it C?

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gmat009: Master | Next Rank: 500 Posts; Posts: 458; Joined: Sun Aug 31, 2008 10:44 amFollowed by: 1 member; Thanked: 3 times

by gmat009 » Thu Oct 09, 2008 11:34 am

rtfact wrote:the answer is C since:

(1) x+y=z --> -x=y-z thus |x|=y-z is true only if x<=0.
for example, if x=1 then according to (1): -1=y-z which contradicts: 1=y-z
insufficient.

(2) x<0 insufficient as you said.

(1+2) sufficient. x<0, therefore in statement (1): -x=y-z, x is positive, which leads us to conclude that |x|=y-z is true.

Thanks......

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vivek.kapoor83: Legendary Member; Posts: 833; Joined: Mon Aug 04, 2008 1:56 am; Thanked: 13 times

by vivek.kapoor83 » Thu Oct 09, 2008 12:07 pm

i have same ques.
If in any ques it is asked mod x = mod y
and nothing about -ve and +ve.
Do we need to prove , x=y AND -x =-y........
I am putting essence on AND...it will be AND (both condition)or OR...means any1 of condition

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cubicle_bound_misfit: Master | Next Rank: 500 Posts; Posts: 246; Joined: Mon May 19, 2008 7:34 am; Location: Texaco Gas Station; Thanked: 7 times

by cubicle_bound_misfit » Thu Oct 09, 2008 2:04 pm

vivek.kapoor83,

there can be different cases for |x| =|y|

x + -

y + -

check how many combos you can have.

Cubicle Bound Misfit

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raju232007: Master | Next Rank: 500 Posts; Posts: 133; Joined: Sat Dec 29, 2007 2:43 am; Thanked: 12 times

by raju232007 » Thu Oct 09, 2008 5:46 pm

Is |x|=y-z

statement 1:

x+y=z
x=z-y( if x>0)
x=y-z( if x<0)

Insufficient

statement 2

x<0

Insufficient

Combining both the statements we have x=y-z for x<0

So the ans should be C..Let me know if you still have any doubts

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