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Please Explain

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by prashanthichennupati » Wed Aug 14, 2013 6:50 am
If x and y are nonzero integers, is (x-1 + y-1)-1 > [(x-1)(y-1)]-1 ?

(1) x = 2y

(2) x + y > 0

Please see my analysis below.Rephrased the question as

Is xy/x+y > xy??

(1) INSUFFICIENT.

Substituted x=2y in the equation which leads to the equation ((2y^2)/(3y))>(2y^2) which means 1/3y >1

When y=-2 and 2 the value is always less than 1
when y=1/3 or 1/6 then value is greater than 1

Hence Insufficient

(2) INSUFFICIENT.

X+Y can take values 1/2, 1, 2 . In first case 1/(X+Y)>1. In second Case 1/(X+Y)=1. In third Case 1/(X+Y)<1. Hence Insufficient.

(3) TOGETHER ALSO INSUFFICIENT

Hence my pick was E. But OA for this problem is Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

Please Explain.

Thanks in Advance.
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Source: — Data Sufficiency |

by Brent@GMATPrepNow » Wed Aug 14, 2013 7:58 am
prashanthichennupati wrote:If x and y are nonzero integers, is (x-1 + y-1)-1 > [(x-1)(y-1)]-1 ?

(1) x = 2y

(2) x + y > 0

Please see my analysis below.Rephrased the question as

Is xy/x+y > xy??

(1) INSUFFICIENT.

Substituted x=2y in the equation which leads to the equation ((2y^2)/(3y))>(2y^2) which means 1/3y >1

When y=-2 and 2 the value is always less than 1
when y=1/3 or 1/6 then value is greater than 1

Hence Insufficient

(2) INSUFFICIENT.

X+Y can take values 1/2, 1, 2 . In first case 1/(X+Y)>1. In second Case 1/(X+Y)=1. In third Case 1/(X+Y)<1. Hence Insufficient.

(3) TOGETHER ALSO INSUFFICIENT

Hence my pick was E. But OA for this problem is Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

Please Explain.

Thanks in Advance.
Presumably, each "-1" in the question is supposed to be a power of -1. As in . . .
"If x and y are nonzero integers, is [x^(-1) + x^(-1)]^(-1) > [(x^-1)(y^-1)]^(-1)?"

For statement 1, everything you did was great, UNTIL you got to the point where you needed to determine whether or not 1/(3y) > 1
As one of your counter-examples, you let y = 1/6, but the question says that y is an integer.
If y is a non-zero integer, then 1/(3y) is ALWAYS less than 1.
For example, if y is negative, then 1/(3y) is negative, which means 1/(3y)< 1
If y is a positive integer, then 1/(3y) < 1
So, statement 1 DOES provide SUFFICIENT information.

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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