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If n is an integer....? Help Please!!

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Source: — Data Sufficiency |

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by Anurag@Gurome » Fri Dec 23, 2011 8:04 pm
gmatpup wrote:If n is an integer, is -3x^n positive?

A. x is odd

B. n is odd


Answer is C

Please explain why A is not the answer?

Thanks again!!

(1) If x = 1 (odd), n = 1 (odd) then -3x^n = -3(1)^1 = negative.
If x = -1 (odd), n = 1 (odd) then -3x^n = -3(-1)^(1) = positive.
No definite answer; NOT sufficient.

(2) Again taking the same examples as in statement 1, we know (2) is also NOT sufficient.

Combining (1) and (2) also, taking the same examples as in 1, we do not know if -3x^n is positive or not; NOT sufficient.

According to me the answer should be E, can you please check it?
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by neelgandham » Sat Dec 24, 2011 4:46 am
If n is an integer, is -3x^n positive?
A. x is odd
If x = -3 and if n = 3, -3x^n is Positive
If x = -3 and if n = 4, -3x^n is Negative
If x = 3 and if n = 3, -3x^n is Negative
If x = 3 and if n = 4, -3x^n is Negative
B. n is odd

If x = -3 and if n = 3, -3x^n is Positive
If x = 3 and if n = 3, -3x^n is Negative
If x = 0 and if n = 3, -3x^n is Neither positive, nor negative

From A and B, x is odd and n is odd.
If x = -3 and if n = 3, -3x^n is Positive
If x = 3 and if n = 3, -3x^n is Negative

IMO E. As Anurag requested, Can you please check ?
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by LalaB » Sat Dec 24, 2011 8:13 am
gmatpup wrote:If n is an integer, is -3x^n positive?

A. x is odd

B. n is odd


Answer is C

Please explain why A is not the answer?

Thanks again!!
hm, may be in A option it is said x is negative?
it would be better :)
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by pemdas » Sat Dec 24, 2011 8:37 am
yes, please check the source

restate -x^n positive?
n is integer
st(1) x is odd, implies x cannot be 0 and following
- positive x returns negative number when n is odd/even;
- negative x returns positive number when n is odd and returns negative number when n is even;
Not Sufficient
st(2) n is odd, implies only power and without x this is Not Sufficient
Combined st(1&2): if x>0 and odd (st.1)along with n is odd (st.2) -3x^n is negative.
If x<0 and odd (st.1)along with n is odd (st.2) -3x^n is positive.
Not Sufficient
gmatpup wrote:If n is an integer, is -3x^n positive?

A. x is odd

B. n is odd


Answer is C

Please explain why A is not the answer?

Thanks again!!
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by CollegeKart » Sat Dec 24, 2011 11:20 am
i agree with Anurag. With the given information the answer should be E
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SO E

by arpan20690 » Tue Dec 27, 2011 12:53 am
-3x^n: its sign depends on the sign of x and nature of n ( whether odd or even).
Sign of x is not mentioned anywhere. So, both conditions are NOT SUFFICIENT individually
and together also. SO E is the right answer.
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by amit28it » Fri Dec 30, 2011 4:22 am
Hello buddy,
Sorry to be here but can anyone suggest me to solve my typical questions related to Decimals for Grade IV . So please help me .
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