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# If m and r are two number on a number line, What is the

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Intern
Joined: 25 Dec 2008
Posts: 41
If m and r are two number on a number line, What is the [#permalink]

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12 Jan 2009, 06:23
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If m and r are two number on a number line, What is the value of r?
A. The distance between r and 0 is 3 times the distance between m and 0
B. 12 is the halfway between m and r

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Manager
Joined: 04 Jan 2009
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12 Jan 2009, 10:54
shobuj40 wrote:
If m and r are two number on a number line, What is the value of r?
A. The distance between r and 0 is 3 times the distance between m and 0
B. 12 is the halfway between m and r

a:r=3m (insuff)
b:m+d=12=r-d or r+d=12=m-d (insuff)

m+d=12
3m-d=12

Both together suff.
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tusharvk

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13 Jan 2009, 04:09
OA is : E
looking fo more discussion
Director
Joined: 14 Aug 2007
Posts: 704

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13 Jan 2009, 06:25
tusharvk wrote:
shobuj40 wrote:
If m and r are two number on a number line, What is the value of r?
A. The distance between r and 0 is 3 times the distance between m and 0
B. 12 is the halfway between m and r

a:r=3m (insuff) OR r = -3*m
b:m+d=12=r-d or r+d=12=m-d (insuff)
2) the average of m & r is 12 i.e. (m+r)/2=12, we can have differnt values for m & r, so insuff

together, substitute r in (2), since r has 2 different values, we still can not find out exact value of r.
E
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Joined: 09 May 2008
Posts: 12
Location: Trieste, Italy

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13 Jan 2009, 09:00
I still can't get how comes E, as I can find an exact value for r.

stmt 1:
r=3m, we have a linear equation with 2 variables, thus INSUFF.

stmt 2:
if 12 is the halfway between r and m, it means that the 12 is the average of r and m.
It means that (r+m)/2=12 => r+m=24.
Still, one linear equation with two variables, thus INSUFF.

Both stmts together:
Substitute m=r/3 in the second equation yields r=18, thus SUFF and my answer is C.

Can someone please explain where my approach is flawed?
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Joined: 04 Jan 2009
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13 Jan 2009, 09:54
alpha_plus_gamma wrote:
tusharvk wrote:
shobuj40 wrote:
If m and r are two number on a number line, What is the value of r?
A. The distance between r and 0 is 3 times the distance between m and 0
B. 12 is the halfway between m and r

a:r=3m (insuff) OR r = -3*m
b:m+d=12=r-d or r+d=12=m-d (insuff)
2) the average of m & r is 12 i.e. (m+r)/2=12, we can have differnt values for m & r, so insuff

together, substitute r in (2), since r has 2 different values, we still can not find out exact value of r.
E

You are right; nothing in A says that r and m>0. But both have to be on the same side of zero (either positive or negative side of zero).
12 being in the middle of the two is sufficient to pinpoint the location of both m and r.
Hence, may be I am questioning the OA.
Is there OE?
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tusharvk

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Joined: 25 Dec 2008
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14 Jan 2009, 04:16
can anyone explain it more elaborately
Manager
Joined: 04 Jan 2009
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14 Jan 2009, 12:17
The best way to resolve is look for GMAT conventions.
In such problems, are we to assume that the numbers are to lie on the positive side of zero.
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tusharvk

GMAT Tutor
Joined: 24 Jun 2008
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14 Jan 2009, 13:09
shobuj40 wrote:
If m and r are two number on a number line, What is the value of r?
A. The distance between r and 0 is 3 times the distance between m and 0
B. 12 is the halfway between m and r

Using both statements, you still have two possibilities:

m = 6, r = 18
m = -12, r = 36.

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Intern
Joined: 04 Nov 2007
Posts: 47

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15 Jan 2009, 02:36
shobuj40 wrote:
If m and r are two number on a number line, What is the value of r?
A. The distance between r and 0 is 3 times the distance between m and 0
B. 12 is the halfway between m and r

Statement I : This statement is insufficient as it only gives us information that r=3m.

Statement II : This statement alone is insufficient as it just says that 12 is half way between m & r. That can be any value of r.

Combined together, the only possible answer for r=18. Hence the answer is C
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15 Jan 2009, 02:41
1
KUDOS
Expert's post
tusharvk wrote:
The best way to resolve is look for GMAT conventions.
In such problems, are we to assume that the numbers are to lie on the positive side of zero.

On the GMAT, do not assume anything. If the question doesn't tell you that the numbers are positive, you'll likely be landing in a trap if you assume they are. For the question above, if you assume r and m are both positive, you'll arrive at the conclusion that the answer is C. It's not C, because m can be negative. The answer is E, as I pointed out above.
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If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com

Intern
Joined: 04 Nov 2007
Posts: 47

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15 Jan 2009, 02:52
IanStewart wrote:
shobuj40 wrote:
If m and r are two number on a number line, What is the value of r?
A. The distance between r and 0 is 3 times the distance between m and 0
B. 12 is the halfway between m and r

Using both statements, you still have two possibilities:

m = 6, r = 18
m = -12, r = 36.

You have an interesting arguement & I believe you are right. What is the OA?
Intern
Joined: 25 Dec 2008
Posts: 41

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15 Jan 2009, 02:58
Ianstewart

thanks and rest Mr tusharvak

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Re: Source GMATPrep   [#permalink] 15 Jan 2009, 02:58
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# If m and r are two number on a number line, What is the

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