Geometry | OG12

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Geometry | OG12

by [email protected] » Wed Sep 26, 2012 7:47 pm
121. In the xy-plane, region R consists of all the points (x,y)
such that 2x + 3y ≤ 6. Is the point (r,s) in region R ?


(1) 3r + 2s = 6
(2) r ≤ 3 and s ≤ 2

Please do not share the OG answer..
Source: — Data Sufficiency |

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by Anurag@Gurome » Wed Sep 26, 2012 7:51 pm
[email protected] wrote:121. In the xy-plane, region R consists of all the points (x,y)
such that 2x + 3y ≤ 6. Is the point (r,s) in region R ?


(1) 3r + 2s = 6
(2) r ≤ 3 and s ≤ 2

Please do not share the OG answer..
(1) 3r + 2s = 6 may or may not lie in region R. So, (1) is NOT SUFFICIENT to answer the question.

(2) If we take r = 3 and s = 2, then the point (3, 2) does not lie in region R.
r ≤ 3 and s ≤ 2 implies we can also take negative values for r and s. If r = -2, s = -3, then (-2, -3) lies in region R.
We don't get a unique answer, so (2) is NOT SUFFICIENT to answer the question.

Combining (1) and (2), if r = 2, s = 0 then (2, 0) lies in region R. But if r = 2/3 and s = 2 then (2/3, 2) lies above the line 2x + 3y = 6, which means (2/3, 2) does not lie in region R. Combining also doesn't give a unique answer.

The correct answer is E.

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by GMATGuruNY » Thu Sep 27, 2012 3:53 am
[email protected] wrote:121. In the xy-plane, region R consists of all the points (x,y)
such that 2x + 3y ≤ 6. Is the point (r,s) in region R ?


(1) 3r + 2s = 6
(2) r ≤ 3 and s ≤ 2

Please do not share the OG answer..
Approach 1:

Question rephrased: Is 2r+3s≤6?

Try to plug in values that satisfy both statements.
Maximize r in one case and s in the other.

r maximized:
r=3 and s=0 satisfy both statements.
Is 2(3) + 3(0) ≤ 6?
YES.

s maximized:
r=2/3 and s=2 satisfy both statements.
Is 2(2/3) + 3(2) ≤ 6?
NO.

Since in the first case the answer is YES and in the second case the answer is NO, the two statements combined are INSUFFICIENT.

The correct answer is E.

Approach 2:

Region R comprises all the points on or below y=(-2/3) + 2.

Statement 1: s = (-3/2)r + 3.
Image
The figure above shows that some points on s=(-3/2)r + 3 lie BELOW y=(-2/3)r + 2, while others lie ABOVE y=(-2/3)r + 2.
INSUFFICIENT.

Statement 2: r≤3 and s≤2.
Image
Inside the green box are points such that r≤3 and s≤2.
Some of the points inside the green box lie BELOW y=(-2/3)r + 2, while others lie ABOVE y=(-2/3)r + 2.
INSUFFICIENT.

Statements 1 and 2 combined:
Image
Inside the green box are points on s=(-3/2)r + 3.
Some of these points lie BELOW y=(-2/3)r + 2, while others lie ABOVE y=(-2/3)r + 2.
INSUFFICIENT.

The correct answer is E.
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by sachindia » Fri Nov 23, 2012 9:42 pm
Mitch, you are indeed a gmatguru :)

what an innovative approach..
Regards,
Sach