DS on equations

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r_walid
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Topic: DS on equations
PostThu Nov 05, 2009 9:56 am Reply with quote
Data sufficiency question on the following:
what is the value of n?

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


please explain your process.
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bryantmichaels
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PostThu Nov 05, 2009 11:26 am Reply with quote
I would say that either equation alone is sufficient, since you have one unknown.
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Abdulla
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PostFri Nov 13, 2009 11:09 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)^2=125


please explain your process.
first stmt. we have quadratic equation, so almost always we will have two solutions. lets check.

n^2+2n=15
n^2+2n-15=0
(n+5)(n-3)=0
n= -5, 3 Insufficient

Second stmt. again .. let's check..
(n+2)(n+2)=125
n^2+4n+4=125
n^2+4n-121=0 we can see that n has two values too, so insufficient

Combined, if we subtract stmt 1 from 2 we will get a linear equation with one variable, so we can solve it.

IMO the answer is C
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enniguy
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PostTue Nov 17, 2009 4:33 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)^2=125


please explain your process.
I strongly think that you have mistyped statement 2. I might be wrong too Smile.
Statement 2 should have been:
2) (n+2)^2=25

In which case, answer is C because,
1) n could be 3 or -5.
2) n could be 3 or -7.
Together, n=3.
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Jarron11
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PostWed Nov 18, 2009 12:34 pm Reply with quote
Agree with enniguy
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grockit_jake
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PostThu Nov 19, 2009 4:46 pm Reply with quote
Right you need both to solve. Instead of solving for the 2 possible values of n for each and then comparing, you can solve both equations in terms of n^2, set equal and solve for n that way.
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