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value of integer n?

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value of integer n?

by mental » Sat Dec 13, 2008 4:53 am
What is the value of integer n?

(I) n(n+2) = 15

(II) (n+2)^n = 125

OA: C

I feel that this question has been posted earlier, but I was unable to locate the discussion.
Also I am unable to guarantee the reliability of the source!
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by mental » Sat Dec 13, 2008 4:58 am
Clearly it is not A:

n(n+2) = 15 = 3*5
n = 3

n(n+2) = 15 = (-5)*(-3)
n = -5

two answers insufficient

II) (n+2)^n = 125

125 = (125)^1 = 5^3

ISNT B Sufficient. only one value satisfying: n=3

Am I missing something?
all the other answers were correct on the test.
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by vishubn » Sat Dec 13, 2008 5:01 am
I give up !! I get differnt IMO

A) n(n+2)=15
we get two differtn values of n
Insuff

B)n=3
(3+2)^3=125

No other value satisfies !!

IMO B


vishu
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by cramya » Sat Dec 13, 2008 4:26 pm
What is the value of integer n
Mental,
Whats the source? I think the OA is wrong if it sates C)

Definitely B) for reasons already stated. 125 being a perfect cube there exists only one positive int 5 which when cubed gives 125. n has to be 3.

Regards,
Cramya
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by vittalgmat » Sat Dec 13, 2008 7:30 pm
I give up.. I cant get the OA.

I think OA is wrong. it should be B.

The problem states n is int.
So n can be either -ve int or +ve int or 0.

n can take only 3 to satisfy stmt2.

Cant use:
1) -ve value say -7 will result in a fraction != 125.
eg (-7+2)^-7 is a fraction.

2) irrational number coz it is stated n is int.

3) fraction coz n is int.

4) any +ve number other than 3: coz the result will not be 125

So I think B is the correct answer..
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by logitech » Sat Dec 13, 2008 7:33 pm
I got the OA!!! and it is b

Guys it is so obvious that given OA is wrong, just smile and move on. We don't have time to waste. Do we ?
LGTCH
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by mental » Sun Dec 14, 2008 4:36 am
Thanks vishu, cramya, vittal and logi.

I was also of the opinion that answer should be B

But mortals like me are never sure of their results!
Thanks for reassuring me on the approach and answer.
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