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What is the value of x ? 1) sqrt(x^4)=9; 2) The average

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What is the value of x ? 1) sqrt(x^4)=9; 2) The average [#permalink] New post 05 Aug 2003, 04:07
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What is the value of x ?

1) sqrt(x^4)=9;
2) The average (arithmetic mean) of x^2, 6x and 3 is -2.
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Re: DS practice #2 [#permalink] New post 05 Aug 2003, 04:20
Konstantin Lynov wrote:
What is the value of x ?

1) sqrt(x^4)=9;
2) The average (arithmetic mean) of x^2, 6x and 3 is -2.


Answer is B

First equation gives us x = +sqrt(3) or - sqrt(3)

Second equation gives a quadratic (x^2+6x+3)/3=-2

or x^2+6x+9=0 Now this has only one root x=-3 which gives us a unique value for x
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You bet... [#permalink] New post 05 Aug 2003, 04:26
Prashant,

Could I ask you to post answers only for now. Let us give other people a chance to try these little challenges out.
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Re: You bet... [#permalink] New post 05 Aug 2003, 04:41
Konstantin Lynov wrote:
Prashant,

Could I ask you to post answers only for now. Let us give other people a chance to try these little challenges out.


As you say chief ! :writer
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 [#permalink] New post 05 Aug 2003, 06:50
Prasant,
I agree with your choice. Either (1) or (2) is sufficient to get the values for x. By the way, recheck the solution you found for x from (1). There's a little mistake in the values of x you found.
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Re: DS practice #2 [#permalink] New post 05 Aug 2003, 07:05
Konstantin Lynov wrote:
What is the value of x ?

1) sqrt(x^4)=9;
2) The average (arithmetic mean) of x^2, 6x and 3 is -2.


Hmmm.
these question look straight out of the GMAT 800 book.
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Re: Prakuda's reply [#permalink] New post 05 Aug 2003, 07:15
Prakuda,

From your answer it follows that either 1 or 2 is sufficient. In other words, it follows that D is the answer. However, it is not. You might need to review your approach to the first choice.

sqrt x^4=9 can be written as x^4/2=9. Simplifying gets us x^2. Now, x can be +3, -3

Now, B is sufficient since the quadratic equation has only one root.
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 [#permalink] New post 05 Aug 2003, 10:07
u r correct. What was I thinking?
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 [#permalink] New post 06 Aug 2003, 02:50
prakuda2000 wrote:
Prasant,
I agree with your choice. Either (1) or (2) is sufficient to get the values for x. By the way, recheck the solution you found for x from (1). There's a little mistake in the values of x you found.


Agreed Prakuda, x is +3 or -3.... I stand corrected
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Great Question [#permalink] New post 06 Aug 2003, 12:49
This is really a great question - one that is of the type that I ALWAYS mess up on the practice tests...but got it this time!!

(A) After some hard work, and remembering the values raised to even powers can be + or -, you get +3 and -3

(B) After solving this FOIL, you get -3 and -3, so you say in your head, "Well this confirms with A that it must be -3", so you mark C.

But indeed it is B alone. Great problem to practice separating the A and B in DS problems!!
Great Question   [#permalink] 06 Aug 2003, 12:49
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