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Data sufficiency

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Source: — Data Sufficiency |
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by gmatmachoman » Thu Apr 08, 2010 1:10 pm
tahitiboy wrote:Is m + z > 0?
1. m-3z> 0
2. 4z-m>0

I think the answer is E. Can someone help?
from st 1:

m> 3Z

Let us take Z=1 ,then m>3.

so m+z >0 ( using st 1 alone)

st 2: 4Z- m>0
z>(m/4)

Let m = -10, then z >(-2.5)

Put those values in m+z >0( It gives a NO)

Try another set of values for st 2:

m =4--->Z>1

Now m+z >0 ( gives a YES)

So st 2 is indefinite.

So pick [spoiler]A!![/spoiler]
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by jackmar » Thu Apr 08, 2010 2:15 pm
gmatmachoman wrote:
tahitiboy wrote:Is m + z > 0?
1. m-3z> 0
2. 4z-m>0

I think the answer is E. Can someone help?
from st 1:

m> 3Z

Let us take Z=1 ,then m>3.

so m+z >0 ( using st 1 alone)

st 2: 4Z- m>0
z>(m/4)

Let m = -10, then z >(-2.5)

Put those values in m+z >0( It gives a NO)

Try another set of values for st 2:

m =4--->Z>1

Now m+z >0 ( gives a YES)

So st 2 is indefinite.

So pick [spoiler]A!![/spoiler]
What if you'd put this in ST1:

z = -5
m > 3z
m > 3*-5
m > -15, m = 1 , 1 + -5 = -4 , m < 0
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by asfa » Thu Apr 08, 2010 2:33 pm
IMO E

Stm 1: M>3Z
if M is pos and Z is pos then the answer is yes
if both are neg then the answer is no.
If M is pos and Z is neg then the answer will vary depending on what numbers you chose.

Stm 2: 4Z>M....Same concept

is there an official answer?
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by analyst218 » Thu Apr 08, 2010 2:50 pm
jackmar wrote:
gmatmachoman wrote:
tahitiboy wrote:Is m + z > 0?
1. m-3z> 0
2. 4z-m>0

I think the answer is E. Can someone help?
from st 1:

m> 3Z

Let us take Z=1 ,then m>3.

so m+z >0 ( using st 1 alone)

st 2: 4Z- m>0
z>(m/4)

Let m = -10, then z >(-2.5)

Put those values in m+z >0( It gives a NO)

Try another set of values for st 2:

m =4--->Z>1

Now m+z >0 ( gives a YES)

So st 2 is indefinite.

So pick [spoiler]A!![/spoiler]
What if you'd put this in ST1:

z = -5
m > 3z
m > 3*-5
m > -15, m = 1 , 1 + -5 = -4 , m < 0
yes A is insufficient since m+z>0 doesn't hold true when both are negative values.
hence E.
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by tahitiboy » Thu Apr 08, 2010 9:09 pm
Thanks everyone. The answer is C, which I cannot figure out why.
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by pops » Thu Apr 08, 2010 9:37 pm
tahitiboy wrote:Is m + z > 0?
1. m-3z> 0
2. 4z-m>0

I think the answer is E. Can someone help?
statement1:
m-3z > 0
insufficient as we cannot say clearly for m+z > 0
put m=4,z=-3 and m=1, z=-3 (so in both m-3z > 0 but m+z is > 0 in one and < 0 in other)

statement2:
4z-m>0
like 1 this is also insufficient

combining both:
add 1 and 2 (since both are positive we can add i.e. positive + positive = positive)
hence, m-3z+4z-m > 0
=> z>0

now since z>0 and m>3z hence m>0
hence we can answer that m+z >0
hence C
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by kstv » Thu Apr 08, 2010 9:40 pm
tahitiboy wrote:Is m + z > 0?
1. m-3z> 0
2. 4z-m>0

I think the answer is E. Can someone help?
1. m> 3z
2. 4z > m or m < 4z
combining (1) and (2)
3z <m < 4z so the value of m lies between 3z and 4z
suppose it is 3.1 z
then m+z = 3.1z + z = 4.1 z
suppouse z = 3.9 z then 4.9 z
so the value is dependent on the sign of m and z
how is it C then cos it is not given m and z are +ve nos.
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by Fiver » Fri Apr 09, 2010 8:15 am
tahitiboy wrote:Thanks everyone. The answer is C, which I cannot figure out why.
Adding the inequalities in both statements:
m - 3z > 0
-m +4z>0
We get z>o and since m-3z> 0, m>3z hence m is also positive and so is m + z
Hence C.
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by reply2spg » Fri Apr 09, 2010 9:34 am
C is correct here very nice question.

Here the question asks whether m + z > 0 means m > -z ........ (P)

St 1 m > 3z. let's put +ve and -ve values.

let's say z = -2 and m = -1..... -1 > -6 does that mean that -1 > 2? from (P). Nope
let's say z = 2 and m = 7..... 7 > 6 does that mean that 7 > -6? from (P). Yes

So st 1 is not sufficient

St 2 4z > m. let's put +ve and -ve values

let's say z = -2 and m = -9..... -8 > -9 does that mean that -9 > 2? from (P). Nope
let's say z = 2 and m = 6..... 8 > 6 does that mean that 6 > -2? from (P). Yes

So st 2 is not sufficient

Now let's see st 1 and 2 and here is the trick

m - 3z > 0
-m +4z>0
----------------
z > 0

I get z > 0 and from statement 1, I know that m-3z>0 it means that m is greater than 0 and greater than z. Therefore m is greater than -z. this is the answer

tahitiboy wrote:Is m + z > 0?
1. m-3z> 0
2. 4z-m>0

I think the answer is E. Can someone help?
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by eaakbari » Sat Apr 10, 2010 1:23 am
Answer is C
This is how I approached it

Statement one
m-3z>0
that is m+z>4z
Hence for m+z>0, 4z>0 which implies z>0
But insuff

Statement two
Not Suff

Combining

adding both equations we get z>0 and from we had seen that if z>0 then it Satisfies

Hence C
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