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Re: If n is an integer, is -3x^n positive?
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15 May 2007, 07:52
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ninomoi wrote:
If n is an integer, is -3x^n positive?
1. x is negative 2. n is odd
pls explain. Thanks
Answer is C
in order for the expression to be positive we have to have x negative (-*-=+)
but we also know that x^n where n is even will give us positive number
-2^2=-2*-2=4 so we have to have n odd
Re: If n is an integer, is -3x^n positive?
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29 Mar 2010, 13:58
Gmat Prep says the answer is C, but I think it is A. Can someone tell me what I am doing wrong?
1. x is negative
So, let x be -1. 1 ^ 2 * - * -3 = 3 1 ^ 3 * - * -3 = 3
If x is negative the answer is always positive. If the problem were -3(x)^n then that answer would be C. However, without the brackets you must distribute the negative after you take x^n...therefore the answer will always be a negative number multiplied by -3 which gives a positive answer.
Re: If n is an integer, is -3x^n positive?
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01 Apr 2010, 13:01
gmatready7 wrote:
Gmat Prep says the answer is C, but I think it is A. Can someone
If x is negative the answer is always positive. If the problem were -3(x)^n then that answer would be C. However, without the brackets you must distribute the negative after you take x^n...therefore the answer will always be a negative number multiplied by -3 which gives a positive answer.
I think it's an issue of order of operations. Exponents come before multiplication so if x = -1 and n is even say 2 Then -3 * -1^2 = -3 * 1 = -3
x = -1 and n is odd say 3 then -3 * -1^3 = -3 * -1 = 3
so A by itself is insufficient.... Please correct me if I am wrong
Re: If n is an integer, is -3x^n positive?
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01 Apr 2010, 14:00
PeterFaulkner wrote:
gmatready7 wrote:
Gmat Prep says the answer is C, but I think it is A. Can someone
If x is negative the answer is always positive. If the problem were -3(x)^n then that answer would be C. However, without the brackets you must distribute the negative after you take x^n...therefore the answer will always be a negative number multiplied by -3 which gives a positive answer.
I think it's an issue of order of operations. Exponents come before multiplication so if x = -1 and n is even say 2 Then -3 * -1^2 = -3 * 1 = -3
x = -1 and n is odd say 3 then -3 * -1^3 = -3 * -1 = 3
so A by itself is insufficient.... Please correct me if I am wrong
But you can raise a negative number to an even power and the answer is still negative. -1^2 = -1. For it to be positive you must use brackets around the -1....(-1)^2 = 1. This is why I chose answer a. Are we to assume there are brackets on the GMAT even though they are not shown?
Re: If n is an integer, is -3x^n positive?
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11 Jan 2016, 21:23
NoHalfMeasures wrote:
If n is an integer, is -3x^n positive? (1) x is negative. (2) n is odd.
pls press kudos if you liked the question
Hi, what does the sign of -3x^n depends on ... 1) sign of x.. 2) value(odd/even) of n, and not on sign of n, as it will turn the x variable in a fraction but will not effect the sign of that fraction or integer..
lets see the statements.. (1) x is negative. we are told of one of the two things required .. insuff
(2) n is odd. we are told of one of the two things required .. insuff
combined both the info is provided ... suff
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Re: If n is an integer, is -3x^n positive?
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17 Jan 2016, 06:51
chetan2u wrote:
NoHalfMeasures wrote:
If n is an integer, is -3x^n positive? (1) x is negative. (2) n is odd.
pls press kudos if you liked the question
Hi, what does the sign of -3x^n depends on ... 1) sign of x.. 2) value(odd/even) of n, and not on sign of n, as it will turn the x variable in a fraction but will not effect the sign of that fraction or integer..
lets see the statements.. (1) x is negative. we are told of one of the two things required .. insuff
(2) n is odd. we are told of one of the two things required .. insuff
combined both the info is provided ... suff
I don't understand -- if x is negative then -3(x) = positive number and -3x^n will be positive -- is it for PEMDAS?
Re: If n is an integer, is -3x^n positive?
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17 Jan 2016, 07:02
lpetroski wrote:
chetan2u wrote:
NoHalfMeasures wrote:
If n is an integer, is -3x^n positive? (1) x is negative. (2) n is odd.
pls press kudos if you liked the question
Hi, what does the sign of -3x^n depends on ... 1) sign of x.. 2) value(odd/even) of n, and not on sign of n, as it will turn the x variable in a fraction but will not effect the sign of that fraction or integer..
lets see the statements.. (1) x is negative. we are told of one of the two things required .. insuff
(2) n is odd. we are told of one of the two things required .. insuff
combined both the info is provided ... suff
I don't understand -- if x is negative then -3(x) = positive number and -3x^n will be positive -- is it for PEMDAS?
That x^n operation must come first?
Hi, x^n operation is not there in PEMDAS.. because x^n is one number.. example 4=2^2 so if we have 7*2^2, it means 7*4, because 2^2 is one number.. same goes for x^n.. hence even sign of n is important.. because power of an even number will make any number positive, even if it is negative.. say x=-2 and n=2.. (-2)^2=-2*-2=4, whereas -2^3=-2*-2*-2=-8, a -ive number.. hope it helps
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Re: If n is an integer, is -3x^n positive?
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07 Oct 2016, 22:01
ninomoi wrote:
If n is an integer, is -3x^n positive?
1. x is negative 2. n is odd
pls explain. Thanks
Answer should be C
For the given statement to be positive x should be negative and n should be odd number St 1 : states that x is negative but we dont know if n is even or odd if n is even insuff if n is odd sufficient so st 1 is insuff St 2: States that n is odd again we dont know the value of x whether positive or negative if positive answer to question is no if negative answer to ques is yes again insuff
Combined sufficient since n is odd and x is negative statement will be positive.
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75% (00:56) correct 
