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What is the value of x ? (1) x3 = 6x − x2 (2) 14x = x3 + 5

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What is the value of x ? (1) x3 = 6x − x2 (2) 14x = x3 + 5 [#permalink] New post 04 Oct 2011, 06:43
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

88% (01:41) correct 13% (00:00) wrong based on 8 sessions
Please help me clarify one of the doubt that i have in the question below:

What is the value of x ?

(1) x3 = 6x − x2

(2) 14x = x3 + 5x2

1. Statement (1) BY ITSELF is sufficient to answer the question, but statement (2) by itself is not.
2. Statement (2) BY ITSELF is sufficient to answer the question, but statement (1) by itself is not.
3. Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, even though NEITHER statement BY ITSELF is sufficient.
4. EITHER statement BY ITSELF is sufficient to answer the question.
5. Statements (1) and (2) TAKEN TOGETHER are NOT sufficient to answer the question, requiring more data pertaining to the problem.

-------------------------------------------------------------------------
Please see my doubt in the immediate post
[Reveal] Spoiler: OA

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Re: What is a value of X [#permalink] New post 04 Oct 2011, 06:48
The explaination that has been given is not wrong. But i solved this question through another method and got C as an ans..

We can solve each of the equation and get following roots:
From 1 : 2, -3
From 2 : 2, -7

i got the above roots by diving the RHS and LHS by x to eliminate one x from both the equations. What the OE is given is that they solved this question WITHOUT eliminating the x and hence got X=0 as another solution. Hence, instead of a single solution of x=2, they got 2 common solutions, i.e. x=0 and x=2.

My doubt is that since my maths days in junior school, it has been taught to divide and remove any redundant data. thats what i did. What's wrong in my approach??
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Re: What is a value of X [#permalink] New post 04 Oct 2011, 06:53
krishnasty wrote:
The explaination that has been given is not wrong. But i solved this question through another method and got C as an ans..

We can solve each of the equation and get following roots:
From 1 : 2, -3
From 2 : 2, -7

i got the above roots by diving the RHS and LHS by x to eliminate one x from both the equations. What the OE is given is that they solved this question WITHOUT eliminating the x and hence got X=0 as another solution. Hence, instead of a single solution of x=2, they got 2 common solutions, i.e. x=0 and x=2.

My doubt is that since my maths days in junior school, it has been taught to divide and remove any redundant data. thats what i did. What's wrong in my approach??


x can be zero in both statements. you ignored that value. the question doesn't state any data (such as x is positive) that suggests that 0 is not a possible option.

clear?
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Re: What is a value of X [#permalink] New post 04 Oct 2011, 07:02
You haven't considered 0 as a possible answer

Statement 1 => x= 0 or 2 or -3
Statement 2 => x= 0 or -7 or 2

Thus even when statements 1 and 2 are taken together => x can still be either 0 or 2 -> which is not sufficient.
Answer - (E)
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Re: What is a value of X [#permalink] New post 04 Oct 2011, 07:30
braxus wrote:
You haven't considered 0 as a possible answer

Statement 1 => x= 0 or 2 or -3
Statement 2 => x= 0 or -7 or 2

Thus even when statements 1 and 2 are taken together => x can still be either 0 or 2 -> which is not sufficient.
Answer - (E)


I am not sure if you got my doubt..i understand that 0 can also be a possibility but when u approach the question, it's general tendency to cancel out x from both side of the equations. and I KNOW that it's not incorrect. And if you solve by cancelling out the Xs from the equations, u wont get 0 as a solution..
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Re: What is a value of X [#permalink] New post 04 Oct 2011, 07:49
you cancel out x only when you know that x is not zero,
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Re: What is a value of X   [#permalink] 04 Oct 2011, 07:49
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What is the value of x ? (1) x3 = 6x − x2 (2) 14x = x3 + 5

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