[neha.visionary]

Originally Posted by bhavin422

To err is human ...
Each one of us make silly errors ...infact most of the math errors on GMAT are avoidable ones ...to learn from them n ace our scores is the purpose of the forum ..Cheers

Thanks Bhavin.
Got your point.
and Yogesh and Bhavin really good discussion.
my doubts are cleared.

[deepakraam]

Solve this

If k is a positive constant and y = |x - k| - |x + k|, what is the maximum value of y?

(1) x < 0

(2) k = 3

[Nipunbans]

y = x - k - x - k => -2k.
I am trying to explain that value of y won't depend on x, it will just depend on k.

(1) Insuff. because we don't know K
(2) suff. becoz value of K can determine value of y.

So, IMO = B

Originally Posted by deepakraam

Solve this

If k is a positive constant and y = |x - k| - |x + k|, what is the maximum value of y?

(1) x < 0

(2) k = 3

[Perceto]

Why dont you check out http://www.GenietTlks.com/ . I found some really useful information there.

[bhavin422]

Originally Posted by deepakraam

Solve this

If k is a positive constant and y = |x - k| - |x + k|, what is the maximum value of y?

(1) x < 0

(2) k = 3

Originally Posted by Nipunbans

y = x - k - x - k => -2k.
I am trying to explain that value of y won't depend on x, it will just depend on k.

(1) Insuff. because we don't know K
(2) suff. becoz value of K can determine value of y.

So, IMO = B

IMO also Ans shd be B ...

But y is not necessarily -2k

If, x<0, then y=2k and if x>0 then y=-2k ...in any case, max of 2k and -2k is 2k since k is +ve ...so we need a def value of k to get max value of y ...

St 1 ; we just know y =2k ...no info about k, not suff
St 2 : max y = 2k = 6 ...suff ...Ans B

[sdt83]

Ders 3 diff. possible values of y..
y=-2k, 2k & -2x
stmt 1.
x<0, clearly not suff.
stmt 2.
k=3, nothing said about x.so insuff.
combining both , possible values of y can be -6,6 and -2*(x<0) .
so insuff..
IMO E

[Nipunbans]

@ sdt83.. can you explain a bit more -- how y = -2x

Originally Posted by sdt83

Ders 3 diff. possible values of y..
y=-2k, 2k & -2x
stmt 1.
x<0, clearly not suff.
stmt 2.
k=3, nothing said about x.so insuff.
combining both , possible values of y can be -6,6 and -2*(x<0) .
so insuff..
IMO E

[sdt83]

my mistake.. ders r 4 diff values for y..
Lets look @ various possible values of y..
1.(x-k)-(x+k)=-2k, when both x-k & x+k are +ve
2.-(x-k)-(-(x+k))=2K, when both x-k & x+k are -ve.
3.x-k+ x+k=2x, when x-k is +ve & x+k is -ve
4.-x+k-x-k=-2x when x-k is -ve & x+k is +ve.
now both d stmts r not suff to ans.
IMO E

[Perceto]

You might ask the same question at GenieTalks

[Eon]

Originally Posted by bhavin422

IMO also Ans shd be B ...

But y is not necessarily -2k

If, x<0, then y=2k and if x>0 then y=-2k ...in any case, max of 2k and -2k is 2k since k is +ve ...so we need a def value of k to get max value of y ...

St 1 ; we just know y =2k ...no info about k, not suff
St 2 : max y = 2k = 6 ...suff ...Ans B

IMO Bhavin is right. If the Q asks for a single value of y then it would be E. But the Q asks for max value , so st 2 should be sufficient..so B