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Ratio of m to n^2

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Ratio of m to n^2

by gmatrant » Thu Sep 02, 2010 5:11 am
if mn not equal to 0, what is the ratio of m to n^2?
1) The ratio of m^2 to 1 is 7/5
2) The ratio of m^2 to n is 7/5

[spoiler]In A, m can be -sqrt(7/5) or +sqrt(7/5)
In B m is +sqrt(7) or m is - sqrt(7)
Not sure how to proceed from here...[/spoiler]
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Source: — Data Sufficiency |
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by Gurpinder » Thu Sep 02, 2010 6:20 am
I would say (B).

M : N^2

(1) M:1 - which I don't think is really important since it doesn't tell us anything about N.

(2) M:N - sqrt/7 : 5^2 <- would be our ratio.

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by Maciek » Thu Sep 02, 2010 8:22 am
hi all!

IMO E
mn is not equal to 0
m/(n^2) = ?
(1)
if the m^2 /1 = 7/5 then m^2 = 7/5 and
m = √(7/5) or m = -√(7/5)
statement 1 alone is INSUFFICIENT
answers A and D are not correct

(2)
if m^2/n = 7/5 then n = (5/7)*m^2 and
m/(n^2) = ?
m/((5/7)*m^2)^2 =
= 49/(25*m^3) = ?
statement 2 alone is INSUFFICIENT
answer B is not correct

(1) & (2)
if the m^2 /1 = 7/5 & m^2/n = 7/5 then n = 1, so
m/(n^2) = m = √(7/5) or -√(7/5)
statements 1 and 2 both are together INSUFFICIENT
answer E is correct

hope it helps!
Best,
Maciek
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by gmatrant » Fri Sep 03, 2010 11:32 pm
The OA is C.
Can someone explain.
Experts can you please take this question?
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by rohit_gmat » Sat Sep 04, 2010 12:57 am
Maciek wrote:(1) & (2)
if the m^2 /1 = 7/5 & m^2/n = 7/5 then n = 1, so
m/(n^2) = m = √(7/5) or -√(7/5)
statements 1 and 2 both are together INSUFFICIENT
answer E is correct
I agree that the answer is E.
Whats the source of this question? Has it been copied correctly?
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by Tani » Sat Sep 04, 2010 9:05 am
Is the second clue m^2/n^2 or m/n^2?
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by Ian Stewart » Sat Sep 04, 2010 10:52 am
Any real GMAT ratio question involving unknowns will always specify that the unknowns are positive. If you knew that both m and n were positive in this question, then the answer would be C. As it stands, the answer is E, since we don't know whether m is positive or negative.
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by HPengineer » Sat Sep 04, 2010 11:26 am
Can you explain the algebra here?

m/(n^2) = m = √(7/5) or -√(7/5) I thought N = 1?
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by rohit_gmat » Sat Sep 11, 2010 7:45 pm
HPengineer wrote:Can you explain the algebra here?

m/(n^2) = m = √(7/5) or -√(7/5) I thought N = 1?
Yes you are right, N=1.
So, m/(n^2) = m/(1^2) = m/1 = m
But the problem is, what is the value of m?
From the statements, all we know is m^2 = (7/5) , which doesn't give us a single value for m.
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