How to solve this one?

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r_walid
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Topic: How to solve this one?
PostThu Nov 05, 2009 11:46 am Reply with quote
Data sufficiency question on the following:
what is the value of n?

1) n(n+2) = 15
2) (n+2)^n=125


please explain your process.
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mridul_dave
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PostThu Nov 05, 2009 12:51 pm Reply with quote
r_walid wrote:
Data sufficiency question on the following:
what is the value of n?

1) n(n+2) = 15
2) (n+2)^n=125

please explain your process.
Statement 1 is not sufficient as it indicates two possible values of n ( 3 , -5)

Statement 2: take log on both sides.

n * log(n+2) = 3*log (5)

This implies n = 3 ( someone please endorse this !)
Therefore Answer is B.
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mjsobo
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PostThu Nov 05, 2009 12:59 pm Reply with quote
hey,
so let's look at statement 1) first:

1) n(n+2) = 15

we can set it up so that n^2+2n-15=0 and see that (n+5)(n-3) = 0, so n is equal to -5 or 3. not suff

in 2) we can quickly see by plugging numbers that n must be 3 so that (3+2)^3 = 125. Because we get only one possible value of n, this statement is sufficient, making the answer B.
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YourDreamTheater
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PostThu Nov 05, 2009 1:02 pm Reply with quote
I would guess B

n(n+2) = 15
n^2 + 2n - 15 = 0
(n-3)(n+5) = 0
n = 3 or -5
NOT SUFFICIENT

(n+2)^n = 125
n*log(n+2) = 3*log(5)
you can't take the log of a negative number... so n=3
so it is SUFFICIENT


What's the OA?
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