GPREP - 1 (Explanation Plzzz..) - Page 2 - The Beat The GMAT Forum

GPREP - 1 (Explanation Plzzz..)

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kshin78: Senior | Next Rank: 100 Posts; Posts: 42; Joined: Tue Jun 17, 2008 1:18 pm; Thanked: 2 times

by kshin78 » Tue Aug 19, 2008 10:57 am

kshin78 wrote:

Why u r considering 'z' & 'm' as positive???
Consider
m= -4, z= -2

Now solve...

1) m-3z>0
-4 + 6 = 2, which is greater than 0

2) 4z-m<0
-8 +4 = -4, which is less than 0

doesn't value for m & z both satisfy 1 as well as 2

Now would u say that combining both statements we get both 'z' and 'm' as negative.
So we can't assume them positive.?????

moreover que doesn't say that m and v are positive...
I'm not assuming anything.....[/quote]

i'm so with you Suyog... i can't seem to figure it out...

the argument here is that m> 0 because z > 0. ok, true if z > 0, but WHY??? We can't assume that z > 0 when there are negative values that holds true for both equations.[/quote]

BTW..just saw this error as part of Sentence correction. it should be "negative values that hold" ... i know this is not a verbal section but just practicing...lol

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nikhilagrawal: Senior | Next Rank: 100 Posts; Posts: 81; Joined: Thu Jun 12, 2008 1:57 pm; Thanked: 1 times

by nikhilagrawal » Tue Aug 19, 2008 11:48 am

I feel that from these eqn:

If a)+b) implies m>0 ie M is positve (we cant take the negative numbers)

from eqn a) I can say m >3z

from eqn b) I can say m <4z

from this we can deduce 3z<m<4z;

So answer shld be C.

Pls let me know if I am wrong .. bcos I can be

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Tue Aug 19, 2008 12:19 pm

Is m+z>0?

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

I agree that the answer should be (E).

Even taking both statements into account, we could choose:

m = 4, z = 1/3, since

1) 4 - 1 > 0
and
2) 4/3 - 4 < 0

to get a "yes" answer, and

m = -1 and z = -5, since

1) -1 - (-15) > 0
and
2) -60 - (-1) < 0

to get a "no" answer.

It's very important to remember that we CANNOT treat inequalities as we do equations.

For example, we cannot simply add or subtract two inequalities, as some have tried to do in this thread. Let's look at a more concrete example:

x + 3 > 0
x + 5 > 0

Clearly, these two statements could both be true (and will be true for all x > -5). However, if we subtract the second from the first, we'd get:

-2 > 0

which obviously makes no sense.

edited because my example need fixin'!

Last edited by Stuart@KaplanGMAT on Wed Aug 20, 2008 10:09 am, edited 1 time in total.

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Suyog: Master | Next Rank: 500 Posts; Posts: 315; Joined: Thu Aug 17, 2006 10:43 pm; Thanked: 23 times

by Suyog » Tue Aug 19, 2008 1:14 pm

Absolutely gr8!!!! :twisted:
A BIG Thank you Stuart

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amitansu: Master | Next Rank: 500 Posts; Posts: 294; Joined: Tue Feb 26, 2008 9:05 pmFollowed by: 1 member; Thanked: 13 times

by amitansu » Tue Aug 19, 2008 8:50 pm

Stuart Kovinsky wrote:
Is m+z>0?

1) m-3z>0
2) 4z-m<0
I agree that the answer should be (E).

It's very important to remember that we CANNOT treat inequalities as we do equations.

For example, we cannot simply add or subtract two inequalities, as some have tried to do in this thread. Let's look at a more concrete example:

x + 3 > 0
x - 5 > 0

Clearly, these two statements could both be true (and will be true for all x > 5). However, if we subtract the second from the first, we'd get:

-2 > 0

which obviously makes no sense.

This is a good learning for me , i agree for sure, that inequalities can't be solved like equations !!

Amit

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4meonly: Legendary Member; Posts: 891; Joined: Sat Aug 16, 2008 4:21 amFollowed by: 1 member; Thanked: 27 times; GMAT Score:660(

by 4meonly » Tue Aug 19, 2008 10:44 pm

I think E.

question: m+z>0? or m>-z?

(1) m-3z>0, or m>3z. So what? They are positive or negative?
(1) 4z-m<0, or m>4z. So what? They are positive or negative? (2) is the same as (1)

(1) and (2)
still insuffucient. E.

Why C?

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kiran.raze: Senior | Next Rank: 100 Posts; Posts: 45; Joined: Sat May 19, 2007 8:38 pm; Thanked: 2 times; GMAT Score:710

by kiran.raze » Wed Aug 20, 2008 9:28 am

Absolutely guys , the point which was causing trouble all along was how did sudhir & amit get to a conclusion than z is>0 ,

because combining the 2 inequalities we get only m>3Z & m>4z which are insufficient to prove z> 0

I guess I still stick to E !!

whats the OA by the way anyone??

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codesnooker: Legendary Member; Posts: 543; Joined: Fri Jan 18, 2008 1:01 am; Thanked: 43 times; GMAT Score:580

Re: GPREP - 1 (Explanation Plzzz..)

by codesnooker » Wed Aug 20, 2008 7:27 pm

raptor84 wrote:IS m+z>0

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

OA C

Hell Raptor84! you have posted wrong question and wasted everyone's time. The second equation that you have posted is wrong. It should be 4z-m > 0

Guys, correct question is posted over here.

https://www.beatthegmat.com/m-z-0-t15944.html

And yes inequalities can be added if they have same sign and (C) is the correct answer.

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