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GMATPrep m+z>0?

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Re: GMATPrep m+z>0?

by logitech » Sat Dec 20, 2008 10:48 am
ddo wrote:Is m+Z>0?

1 m-3z>0
2 4z-m>0

which is the best way to approach this Q? I picked nbrs but was really time consuming.
If you look at both statements, they only compare which one is greater than which...but we need to know their signs to find out whether m+z is greater than zero so dont even think A , B or D

this is a C/E question.

Lets check for C:

1 m-3z>0
2 4z-m>0
+
-----------------------
z>0 AHA!!

and we know that m>3z so m should be positive too

so m+z>0

C
LGTCH
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by cramya » Sat Dec 20, 2008 12:01 pm
Stmt I

m > 3z

If z is positive then m+z > 0
If z is negative then m+z can be less than 0 or greater than 0

INSUFF

Stmt II

4z>m

Similar explanation as above

Stmt I and II

m>3z
4z>m

Add inequalities facing same direction

m+4z>m+3z
m+3z+z>m+3z

z>0 therefore m>0 so m+z is positive

SUFF

Choose C)
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by anshulseth » Mon Apr 06, 2009 5:07 am
I used the following reasoning and got to a diff answer.

a. m-3z>0
b. 4z-m>0

combining both
m>3z
and 4z>m

thus 3z<m<4z.

Thus m can be any value between 3z and 4z. Lets assume 3.5z.
So, m+z = 3.5 z + z = 4.5 z

Now, as we dont know anything about z, whether it is positive, negative or zero, we can't answer the question.
So, E.

Please point out any flaw in my reasoning.
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by bsandhyav » Wed Aug 12, 2009 11:17 pm
anshulseth wrote:I used the following reasoning and got to a diff answer.

a. m-3z>0
b. 4z-m>0

combining both
m>3z
and 4z>m

thus 3z<m<4z.

Thus m can be any value between 3z and 4z. Lets assume 3.5z.
So, m+z = 3.5 z + z = 4.5 z

Now, as we dont know anything about z, whether it is positive, negative or zero, we can't answer the question.
So, E.

Please point out any flaw in my reasoning.

I did exactly the same thing and got the answer wrong. Can anybody pls explain wot is wrong with the approach!!

Experts pls help !
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by tohellandback » Wed Aug 12, 2009 11:23 pm
bsandhyav wrote:
anshulseth wrote:I used the following reasoning and got to a diff answer.

a. m-3z>0
b. 4z-m>0

combining both
m>3z
and 4z>m

thus 3z<m<4z.

Thus m can be any value between 3z and 4z. Lets assume 3.5z.
So, m+z = 3.5 z + z = 4.5 z

Now, as we dont know anything about z, whether it is positive, negative or zero, we can't answer the question.
So, E.

Please point out any flaw in my reasoning.

I did exactly the same thing and got the answer wrong. Can anybody pls explain wot is wrong with the approach!!

Experts pls help !
"we dont know anything about z"
but we know don't we?
you got the equation,
3z<m<4z
i.e. 4z>3z..i.e only when z is positive
if m were negative, the equation would be 3z>m>4z.

Hope I am clear
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by bsandhyav » Wed Aug 12, 2009 11:39 pm
Can anybody clear this concept for me?

we have 3z<m<4z; the signs will remain the same if z is +ve.

But what if z is -ve?

will it be (1) 3z>m>4z??? or remain (2) 3z<m<4z???

In case of (1) if z =-1;then -3>m>-4 which is possible and the answer would be E

However in case of (2) if z=-1;then -3<m<-4 which is an impossible case.
So answer will be C.

I do realise the (2) is correct but can sombody pls help me reason this out?
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by lav » Thu Aug 13, 2009 1:39 am
To get info about z just add these two inequalities
a. m-3z>0
b. 4z-m>0

you get z>0
HTH
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by arora007 » Mon Jun 28, 2010 2:40 am
bsandhyav wrote:Can anybody clear this concept for me?

we have 3z<m<4z; the signs will remain the same if z is +ve.

But what if z is -ve?
Generally

if z is positive then

3z<m<4z

in case z were negative then

4z<m<3z

try and plug values

if z=1 then for the inequality that can be correct is 1 as 3< m <4 i.e. 3<4

however if we were to plug in 1 into inequality 2 it would be 4<m<3 i.e. 4<3 which is illogical

similarly

if z= -1 then the inequality -4<m<-3 i.e. -4<-3 would hold water whereas -3<m<-4 would fail as -3<-4 is illogical.

hope you understood?
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by Testluv » Mon Jun 28, 2010 4:45 pm
https://www.beatthegmat.com/is-m-z-0-t48172.html#247288
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