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According to GMAT Prep, answer is C. If we consider both the statements, it will end up as 3z<m<4z. How can we confirm that m+z>0 until and unless we know the value of z (+ve or -ve)

Re: GMAT Prep quant Doubt [#permalink]
14 Oct 2011, 12:12

1

This post received KUDOS

rvind wrote:

Is m+z > 0? 1) m-3z >0 2) 4z-m >0

According to me, the answer should be E.

According to GMAT Prep, answer is C. If we consider both the statements, it will end up as 3z<m<4z. How can we confirm that m+z>0 until and unless we know the value of z (+ve or -ve)

Pls help me on this one.

If you consider z negative than equation will be -> 3z>m>4z consider z=-1, and assume m= - 3.5, these values doesn't fit the above equation. Hence negative value is not be a right for z amd m in this question. hence, C. _________________

----------------------------------------------------------------------------------------- What you do TODAY is important because you're exchanging a day of your life for it! -----------------------------------------------------------------------------------------

Re: GMAT Prep quant Doubt [#permalink]
14 Oct 2011, 12:28

Ajay369 wrote:

If you consider z negative than equation will be -> 3z>m>4z consider z=-1, and assume m= - 3.5, these values doesn't fit the above equation. Hence negative value is not be a right for z amd m in this question. hence, C.

Ajay,

Though now that you have old that 3z<m<4z can only imply positive value of z i fully agree and feel i have always known this fact, but otherwise I wouldn't have picked this relation if i saw in question format. thanks so much for this.

however i did solved this question and got the right answer c but through different method(which took me about 1.75mins), can you tell me if my way was right. I solved like this Is m+z > 0? 1) m-3z >0 2) 4z-m >0

as both inequalities have same side, I added both LHS and RHS sides to get z > o

After that I multiplied inequality 1 by 4 to get 4m -12z >0 and inequality 2 by 3 to get 12z -3m..........again I added both t get m > 0.....can you tell me if my multiplying any inequality by a positive number is correct or not ? especially when RHS side contains 0 ?

Re: GMAT Prep quant Doubt [#permalink]
14 Oct 2011, 16:38

Aj85 wrote:

Ajay369 wrote:

If you consider z negative than equation will be -> 3z>m>4z consider z=-1, and assume m= - 3.5, these values doesn't fit the above equation. Hence negative value is not be a right for z amd m in this question. hence, C.

Ajay,

Though now that you have old that 3z<m<4z can only imply positive value of z i fully agree and feel i have always known this fact, but otherwise I wouldn't have picked this relation if i saw in question format. thanks so much for this.

however i did solved this question and got the right answer c but through different method(which took me about 1.75mins), can you tell me if my way was right. I solved like this Is m+z > 0? 1) m-3z >0 2) 4z-m >0

as both inequalities have same side, I added both LHS and RHS sides to get z > o

After that I multiplied inequality 1 by 4 to get 4m -12z >0 and inequality 2 by 3 to get 12z -3m..........again I added both t get m > 0.....can you tell me if my multiplying any inequality by a positive number is correct or not ? especially when RHS side contains 0 ?

@Aj85 - your method is also right but as you said, it takes time. while solving any inequality i always prefer to put relevant numerical values and check. In this question its very easy to figure out that when z is negative the equation is -> 3z>m>4z and when z is positive than equation is -> 3z<m<4z. Put z=-1, and m= - 3.5 and z=1, and m= 3.5 respectively.

Hope it helps. _________________

----------------------------------------------------------------------------------------- What you do TODAY is important because you're exchanging a day of your life for it! -----------------------------------------------------------------------------------------