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Inequality

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Inequality

by jayanti » Mon Aug 08, 2011 12:45 am
If x > 3 and y > -1, then which of the following is always true:

A) x < 3y

B) -x < 3y

C) xy < -3

D) -x > 3y

E) x < -3y
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by pemdas » Mon Aug 08, 2011 3:00 am
x>-3y will always be true, hence b
jayanti wrote:If x > 3 and y > -1, then which of the following is always true:

A) x < 3y

B) -x < 3y

C) xy < -3

D) -x > 3y

E) x < -3y
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by jayanti » Mon Aug 08, 2011 5:01 am
Hi, could you pls explain it as how???

Thanks a lot
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by GmatKiss » Mon Aug 08, 2011 6:39 am
IMO:B,

just substitute values.

x can be (4,5,6,.....n)
y can be (0,1,2,3,....m)

B => -x < 3y

1) let x be 4 and y be 0,
-4 < 0
2) let x be 4 and y be 1,
-4 < 3

Hence B! Hope it helps.
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by Frankenstein » Mon Aug 08, 2011 6:43 am
jayanti wrote:Hi, could you pls explain it as how???
Hi,
x>3
y>-1. Multiply this inequality with (-3). Multiplication by a negative quantity changes the sign of inequality.
So, -3y < (-1)*(-3)
=> -3y < 3
x > 3(x is always greater than 3) and -3y < 3(-3y is always less than 3)
So, x > -3y
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by gmatboost » Mon Aug 08, 2011 8:18 am
I agree with the explanation, but I think the more natural one to multiply by the negative number is the one with x:
x > 3
-x < -3

y > -1
3y > -3

-x < -3 < 3y matches the way B is written
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by Frankenstein » Mon Aug 08, 2011 8:25 am
Hi,
Agreed. Sorry I haven't seen the question properly. I only saw two posts:
x>-3y will always be true, hence
and a reply to that
Hi, could you pls explain it as how???
So, explained that part and didn't bother about the actual question.
Cheers!

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