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DS question

by greatchap » Wed Sep 10, 2008 3:57 am
Hi Guys,

I came across the following question and got stuck.

Q-A) If x - y > 10, is x - y > x + y ?

(1) x = 8
(2) y = -20

OA is D (Each statement alone is suff)

I wonder why and how to solve it ??

Thanks,

GR
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Source: — Data Sufficiency |
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by GG04 » Wed Sep 10, 2008 5:45 am
Hi GR,

X-Y > 10. The simplest way to do this would be to start with the first Statement and substiute the value. If x = 8, then the only way that

8-Y will be greater than 10, is if Y is a negative number like (-3) onwards..
so, 8-(-3) = 11 is greated than 10. So X + Y will be 8+(-3) which is 5.
Basically for any negative value of Y -3 onwards, X-Y will be a positive number definitely larger than X+Y(whose value will decrease larger the absolute value for Y)

Similarly, you can reason out with the second statement Y = -20
X-Y>10 is same as X-(-20) >10 same as X+20 >10 or X > -10. So
assuming value of X to be -11 , X+Y will be -11+(-20) = -31

So hence each statement by itself is sufficient to tell us if X-Y>X+Y
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thx

by greatchap » Wed Sep 10, 2008 8:19 am
Thanks GG04 for the explanation. Now I got it. :)
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Re: DS question

by sudi760mba » Wed Sep 17, 2008 4:44 am
greatchap wrote:Hi Guys,

I came across the following question and got stuck.

Q-A) If x - y > 10, is x - y > x + y ?

(1) x = 8
(2) y = -20

OA is D (Each statement alone is suff)

I wonder why and how to solve it ??

Thanks,

GR
I agree with GG04; Princeton Review recommends that we look and evaluate each statement individually. so

(1) 8-y> 10; The only way this is possible is if y was negative because if y was 0, then it would be 8 > 10 which is not right. or if y was 1 then it would be 7 > 10 which is also wrong. So only y being -3, 8-(-3) > 11.

8-(-3) > 8 -3 . This can be sufficiently answered since we know x and y.

(2) x - (-20) > 10 x could be -9 which would mean 11>10 and in the same manner since we know x and y, this is sufficient.

so hence (D)
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by rooroo0312 » Mon Sep 29, 2008 1:05 am
hi - another efficient way to attack this problem is to notice that
the question stem:
x - y > x + y ?

is the same as -y > y ?

this will allow you to determine that (2) is sufficient off the bat as
-(-20) > -20

For (1), if x=8, then y < 8-10 or y < -2.
Multiply each side by -1 and u get -y > 2.
So, u c that -y > y (sufficient)

answer D
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