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value of n

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by gmatmachoman » Fri Mar 12, 2010 9:53 am
What is the value of the integer n?
(1) n(n + 2) = 15
(2) (n + 2)n = 125
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Source: — Data Sufficiency |
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by mohit11 » Fri Mar 12, 2010 10:36 am
What is the value of the integer n?
(1) n(n + 2) = 15

1 tells us that n is odd, since for the product to be odd n and n+2 need to be odd.

only integer values that would satisfy the given equation is 3 * 5

(2) (n + 2)n = 125

Same reasoning as above, n has to be odd. However there is no odd integer value that would satisfy the above equation.

My answer is A

Though, if i am slightly inclined towards D

OA?
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by thephoenix » Fri Mar 12, 2010 10:46 am
gmatmachoman wrote:What is the value of the integer n?
(1) n(n + 2) = 15
(2) (n + 2)n = 125
a is the ans
1) n=3

2) we are not getting any real value i guess the statement is not as per the GMAT stndard
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by gmatmachoman » Fri Mar 12, 2010 11:32 am
thephoenix wrote:
gmatmachoman wrote:What is the value of the integer n?
(1) n(n + 2) = 15
(2) (n + 2)n = 125
a is the ans
1) n=3

2) we are not getting any real value i guess the statement is not as per the GMAT stndard
Yeah Phenox,same thought I had...this was from GMAT SETS..
OA is A...

But ,I have seen somewhere in a quadriatic equation where D<0( so no real roots)
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by papgust » Fri Mar 12, 2010 6:32 pm
thephoenix wrote:
gmatmachoman wrote:What is the value of the integer n?
(1) n(n + 2) = 15
(2) (n + 2)n = 125
a is the ans
1) n=3

2) we are not getting any real value i guess the statement is not as per the GMAT stndard

Can't we assume n to have -ve values as well? The question says n is just an integer. An integer can be +ve or -ve.

-5 * -3 = 15

5 * 3 = 15

Two different values of n.
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by mohit11 » Fri Mar 12, 2010 8:01 pm
papgust wrote:
thephoenix wrote:
gmatmachoman wrote:What is the value of the integer n?
(1) n(n + 2) = 15
(2) (n + 2)n = 125
a is the ans
1) n=3

2) we are not getting any real value i guess the statement is not as per the GMAT stndard

Can't we assume n to have -ve values as well? The question says n is just an integer. An integer can be +ve or -ve.

-5 * -3 = 15

5 * 3 = 15

Two different values of n.

for -5 * -3 = 15, we are assuming that n = -3 , in that case n+2 = -1 not -5 . hence -3 *-5 cannot equate to 15 in this case

are you sure OA is A? I searched this question of some other forums after my reply they have a different OA
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by papgust » Fri Mar 12, 2010 8:16 pm
We can assume n to be -5.
(-5 + 2) = -3. So, -5 * -3 = 15.

What is wrong with this?
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by mohit11 » Fri Mar 12, 2010 8:49 pm
Good Point.. ..:)
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by Phirozz » Sat Mar 13, 2010 12:15 am
gmatmachoman wrote:What is the value of the integer n?
(1) n(n + 2) = 15
(2) (n + 2)n = 125
1. n can be either 3 or -5
2. there is no such value of n exists

So it cannot be answered even after combining both
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by gmatmachoman » Sat Mar 13, 2010 2:38 am
Phirozz wrote:
gmatmachoman wrote:What is the value of the integer n?
(1) n(n + 2) = 15
(2) (n + 2)n = 125
1. n can be either 3 or -5
2. there is no such value of n exists

So it cannot be answered even after combining both
Agreed ...N can take those (3 or -5) values.
So St1 is insufficient.

& st 2 is insufficient as there is no real roots!

SO it shuld be E!!
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by kstv » Sat Mar 13, 2010 8:25 am
What is the value of the integer n?
(1) n(n + 2) = 15
(2) (n + 2)n = 125

(1) If n is +ve , n can be 5,3
n is -ve , n is -5 Insufficient.
(2) (n+2)n = 125 => n²+2n-125= 0
we know if the eq is of the form ax²+bx +c = 0
the roots are -b x = - b ± √(b2- 4ac) / 2a
√(b2- 4ac) in this equation will not give us intergers as roots as it is √(2 ² - 4*1* (-125)) =√4+4*125=2√(124)
Insufficient.

Seems I am going tangent or something wrong with the Q.
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by Stuart@KaplanGMAT » Sat Mar 13, 2010 1:05 pm
gmatmachoman wrote:What is the value of the integer n?
(1) n(n + 2) = 15
(2) (n + 2)n = 125
As soon as we determine that (2) has no integer roots, we determine one other thing:

this is NOT a question that would ever appear on the GMAT.

Every DS value question must have at least 1 viable value (by the rules of the test).

What's the source?
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by gmatmachoman » Sun Mar 14, 2010 6:42 am
Stuart,

I am really sorry for saying this..I forgot the source...Else I wuld have posted it...Plz !
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