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IS X < Y

Expert replies
Source: — Data Sufficiency |

by cans » Mon Sep 12, 2011 9:43 am
X,Y >1
a) x^2 < xy + x.
x(x-y)<x. as x>1, x-y<1.
insufficient
b) xy/(y)(y-1) <1 or x< y-1
x-y < -1. <0
x<y
Sufficient
IMO B
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by [email protected] » Mon Sep 12, 2011 10:22 am
cans wrote:X,Y >1
a) x^2 < xy + x.
x(x-y)<x. as x>1, x-y<1.
insufficient
b) xy/(y)(y-1) <1 or x< y-1
x-y < -1. <0
x<y
Sufficient
IMO B
WHY DID YOU CROSS MULTIPLY Y-1 AND 1 IN OPTION B, WITHOUT CHANGING SIGN. I THINK THIS IS WRONG. WE ARE NOT SURE WHETHER Y-1 IS POSITIVE OR NEGATIVE
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by knight247 » Mon Sep 12, 2011 2:27 pm
@sandeep
Because y-1 is +ve. It is given that y>1. If y is greater than 1 then subtracting 1 from it y will still keep it positive.
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