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SAM
 
 

If -2x > 3y, is x negative?

by SAM Wed May 21, 2008 12:42 pm

If -2x > 3y, is x negative ?

1)y > 0

2)2x + 5y - 20 = 0

Answer is D. Can anybody please explain how the 2nd option holds true ?
sanj
 
 

by sanj Thu May 22, 2008 4:43 pm

-2x>3y or 2x+3y<0

1 y>0 => x<0 suff

2 (2x+3y)+2y=20 =>y>0 ie x<0 suff
D
RonPurewal
Students
 
Posts: 19744
Joined: Tue Aug 14, 2007 8:23 am
 

If -2x > 3y, is x negative?

by RonPurewal Fri May 23, 2008 5:47 am

SAM Wrote:If -2x > 3y, is x negative ?

1)y > 0

2)2x + 5y - 20 = 0

Answer is D. Can anybody please explain how the 2nd option holds true ?


first off, an admonishment: please follow the rules when posting questions.
your title should consist of the first 8 words (approximately) of the problem. since i am a true gentleman with a big heart, i have changed the title of this thread (and your other one) for you, but please title your posts correctly from now on.

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the above solution takes a bit of ingenuity; here's a more ground-level solution.
notice that there's a '2x' in the inequality given in the question prompt, and another '2x' in statement 2. this is a fine opportunity for substitution.
so, SOLVE both things for the '2x':
divide the inequality by -1 --> 2x < -3y
isolate the '2x' in statement (2) --> 2x = -5y + 20
substitute --> -5y + 20 < -3y
solve --> 20 < 2y
10 < y
y > 10
which means
-2x > 3y > 30
-2x > 30
x < -15
sufficient

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you can theoretically use plug-in-numbers on this problem, but it's much more trouble than is worthwhile to discuss.