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Is it Ok to take the roots first?For example, in question 1

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Is it Ok to take the roots first?For example, in question 1 [#permalink] New post 28 Aug 2010, 13:49
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Is it Ok to take the roots first?For example, in question 1 the roots for statement 1 are 0 and 5. For statement II, 0 and -5

Data sufficiency
1) Is X=5?

(I) x^2 – 5x = 0
(II)2x^2 + 10x= 0



2) Is x = y?

(I) |x-2|= 5
(II) y^2 – 4y – 21=0
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Re: DS Inequalities I [#permalink] New post 28 Aug 2010, 14:16
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briandoldan wrote:
Is it Ok to take the roots first?For example, in question 1 the roots for statement 1 are 0 and 5. For statement II, 0 and -5

Data sufficiency
1) Is X=5?

(I) x^2 – 5x = 0
(II)2x^2 + 10x= 0



2) Is x = y?

(I) |x-2|= 5
(II) y^2 – 4y – 21=0


I'm not sure that I understand your question... But as for the problems:

Is x=5?

(1) x^2-5x=0 --> x=0 OR x=5. Not sufficient, to answer whether x=5.

(2) 2x^2+10x=0 --> x=0 OR x=-5. Here we know that x\neq{5}, hence sufficient.

Answer: B.

Is x = y?

(1) |x-2|= 5. Clearly insufficient as no info about y. But from this statement we know that either x=7 or x=-3.

(2) y^2-4y-21=0. Clearly insufficient as no info about x. But from this statement we know that either y=7 or y=-3.

(1)+(2) Now, it's possible that both x and y equal to -3 (or 7) and in this case answer would be YES: x=y BUT it's also possible x to be -3 and y to be 7 (or vise-versa) and in this case answer would be NO: x\neq{y}. Two different answers to the question, hence not sufficient.

Answer: E.

Hope it helps.
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Re: DS Inequalities I [#permalink] New post 28 Aug 2010, 14:23
Bunuel wrote:
briandoldan wrote:
Is it Ok to take the roots first?For example, in question 1 the roots for statement 1 are 0 and 5. For statement II, 0 and -5

Data sufficiency
1) Is X=5?

(I) x^2 – 5x = 0
(II)2x^2 + 10x= 0



2) Is x = y?

(I) |x-2|= 5
(II) y^2 – 4y – 21=0


I'm not sure that I understand your question... But as for the problems:

Is x=5?

(1) x^2-5x=0 --> x=0 OR x=5. Not sufficient, to answer whether x=5.

(2) 2x^2+10x=0 --> x=0 OR x=-5. Here we know that x\neq{5}, hence sufficient.

Answer: B.

Is x = y?

(1) |x-2|= 5. Clearly insufficient as no info about y. But from this statement we know that either x=7 or x=-3.

(2) y^2-4y-21=0. Clearly insufficient as no info about x. But from this statement we know that either y=7 or y=-3.

(1)+(2) Now, it's possible that both x and y equal to -3 (or 7) and in this case answer would be YES: x=y BUT it's also possible x to be -3 and y to be 7 (or vise-versa) and in this case answer would be NO: x\neq{y}. Two different answers to the question, hence not sufficient.

Answer: E.

Hope it helps.



Thanks a lot Bunuel. It helped a lot. =)

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Re: DS Inequalities I [#permalink] New post 29 Aug 2010, 20:56
Bunuel, For the 1st question, I did not understand the highlighted part. How do we know that x is not equal to -5?


(2)2x^2 + 10x = 0 --> x = 0 or x = -5. [highlight]Here we know that x # 5[/highlight], hence sufficient
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Re: DS Inequalities I [#permalink] New post 29 Aug 2010, 21:02
seekmba wrote:
Bunuel, For the 1st question, I did not understand the highlighted part. How do we know that x is not equal to -5?


(2)2x^2 + 10x = 0 --> x = 0 or x = -5. [highlight]Here we know that x # 5[/highlight], hence sufficient


the question is : Is x = 5

(2)2x^2 + 10x = 0 --> x = 0 or x = -5.

=> x is not equal to 5. Hence it is sufficient to answer the question.
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Re: DS Inequalities I [#permalink] New post 29 Aug 2010, 21:05
I got so lost in the options that completely forgot abt the original question. thats silly... thanks a bunch.
Re: DS Inequalities I   [#permalink] 29 Aug 2010, 21:05
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