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sos

by krbharat » Sat Apr 17, 2010 1:57 am
Question # 35
Is x + y > 0 ?
(I) x² - y² > 1
(II) x/y + 1 > 0

(A) Statement (I) ALONE is sufficient, but statement (II) alone is not sufficient

(B) Statement (II) ALONE is sufficient, but statement (I) is not sufficient

(C) BOTH statements TOGETHER are sufficient, but NEITHER statement alone is sufficient

(D) Each statement ALONE is sufficient

(E) Statements (I) and (II) TOGETHER are NOT sufficient

[spoiler]my Answer : B
Actual Answer : E

Explanation
From statement I x² - y² > 1
This can be written as (x + y)(x - y) > 1
There is no other available information to determine if (x + y) is greater than or less than 0.
Thus statement 1 alone is not sufficient to answer the question.

From statement 2, x/y + 1 > 0 or (x + y)/y > 0.
This will be true when either both x + y > 0 and y > 0 or x + y < 0 and y < 0.
Since there is no other available information, this statement alone is also not sufficient to answer the question.

Combining the two statements also we do not get any definite information about, x, y or x + y.
Thus the two statements together are also not sufficient to answer the question.
Therefore, we cannot say for sure whether x + y> 0.

Hence (E) is the correct answer.[/spoiler]
Source: — Data Sufficiency |

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by krbharat » Sat Apr 17, 2010 1:58 am
krbharat wrote:Question # 35
Is x + y > 0 ?
(I) x² - y² > 1
(II) x/y + 1 > 0

(A) Statement (I) ALONE is sufficient, but statement (II) alone is not sufficient

(B) Statement (II) ALONE is sufficient, but statement (I) is not sufficient

(C) BOTH statements TOGETHER are sufficient, but NEITHER statement alone is sufficient

(D) Each statement ALONE is sufficient

(E) Statements (I) and (II) TOGETHER are NOT sufficient

[spoiler]my Answer : B
Actual Answer : E

Explanation
From statement I x² - y² > 1
This can be written as (x + y)(x - y) > 1
There is no other available information to determine if (x + y) is greater than or less than 0.
Thus statement 1 alone is not sufficient to answer the question.

From statement 2, x/y + 1 > 0 or (x + y)/y > 0.
This will be true when either both x + y > 0 and y > 0 or x + y < 0 and y < 0.
Since there is no other available information, this statement alone is also not sufficient to answer the question.

Combining the two statements also we do not get any definite information about, x, y or x + y.
Thus the two statements together are also not sufficient to answer the question.
Therefore, we cannot say for sure whether x + y> 0.

Hence (E) is the correct answer.[/spoiler]


this is how i got b
x/y+1>0
x/y>-1
x>-y
x+y>0

tell me where i went wrong in the above solution.

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by kstv » Sat Apr 17, 2010 5:05 am
x/y+1>0
x/y>-1
x>-y
x+y>0

the bold part is where u went wrong.
x and y are unknown terms
in eq involving inequality unlike = operations
it is not possible to multiply or divide by an unknown
y may be a + or - ve like x
multiplying or dividing by -ve the operation will flip
if x = 2 and y = -3 2/-3 + 1 > 0 2/-3 > -1
but 2>3 is absurd
but multiply by -3 2 < 3
> sign flips to <

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by Fiver » Sat Apr 17, 2010 5:22 am
krbharat wrote:

this is how i got b
x/y+1>0
x/y>-1
x>-y
x+y>0

tell me where i went wrong in the above solution.
Adding to kstv's contribution-In the highlighted part above you are assuming that y>0, which is partly right;
however we also need to account for the possibility that 'y' may be negative.
Hence we need to flip the inequality sign when doing so.

working hereunder:

x/y>-1
when y<0
x<-y
Hence x can be positive value such that x/y is a negative fraction less than 1 or x could also be a negative number, making x/y a positive number.

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by ansumania » Sun Apr 18, 2010 6:15 am
what is the OA?

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by akhpad » Sun Apr 18, 2010 8:08 am
Question # 35
Is x + y > 0 ?
(I) x² - y² > 1
(II) x/y + 1 > 0

Statement 1:
(x-y)(x+y) > 1

x = 3, y = 2, x+y = 5, x-y = 1
x = -3, y = -2, x+y = -5, x-y = -1
Insufficient

Statement 2:
(x+y)/y > 0

x+y > 0 and y > 0
x+y < 0 and y < 0
Insufficient

Statement 1 and 2:
x+y > 0 or x+y < 0
Insufficient

Answer: E