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please explain this question

This topic has 2 expert replies and 1 member reply
sana.noor Legendary Member Default Avatar
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please explain this question

Post Fri Aug 23, 2013 5:27 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    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

    OA is E

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    ganeshrkamath Master | Next Rank: 500 Posts
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    Post Fri Aug 23, 2013 6:40 am
    sana.noor wrote:
    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

    OA is E
    The region extends to the line 2x + 3y = 6
    3y = -2x + 6
    y = (-2/3)x + 2

    ttp://postimg.org/image/otohoog5d/" target="_blank">

    Statement 1: From the figure it is clear that not all the points on this line fall under the shaded region.

    Statement 2: Again from figure we see that this statement alone is insufficient.

    Combination: Again insufficient.

    Choose E

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    Post Fri Aug 23, 2013 7:24 am
    sana.noor wrote:
    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

    I see that ganeshrkamath already posted a graphical solution. Since I finally just finished my solution, I'll post it as well, since it describes a few steps in between.

    Target question: Is the point (r, s) in region R?

    Given: Region R consists of all the points (x,y) such that 2x + 3y <6
    So, what does Region R look like?
    To find out, let's first graph the EQUATION, 2x + 3y = 6
    ttp://postimg.org/image/t6q2in011/" target="_blank">

    Since Region R is described as an INEQUALITY, we can choose any point on the coordinate plane to test whether or not it is in Region R. An easy point to test is (0,0).
    So, does x=0 and y=0 satisfy the inequality 2x + 3y <6? YES
    2(0) + (3)(0) is less than or equal to 6.
    So, the point (0,0) is in Region R. More importantly, EVERY POINT on the same side of the line will also be in Region R.
    ttp://postimg.org/image/iz7j68dt1/" target="_blank">

    Statement 1: 3r + 2s = 6
    The target question refers to the point (r, s)
    In other words, the x-coordinate is r and the y-coordinate is s.
    So, all of the points (r, s) that satisfy the above equation can be found on the line 3x + 2y = 6
    In other words, statement 1 tells us that the point (r,s) lies somewhere on the red line below.
    ttp://postimg.org/image/vckdd53hh/" target="_blank">
    As you can see, some points are in Region R, and some points are not in Region R
    Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

    Statement 2: r < 3 and s < 2
    There are many points that satisfy this condition.
    In fact, the point (r,s) can be ANYWHERE inside the red box shown below.
    ttp://postimg.org/image/bx9lk1a79/" target="_blank">
    As you can see, some points are in Region R, and some points are not in Region R
    Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

    Statements 1 and 2 combined
    When we combine the statements, we are saying that the point (r,s) is on the red line (2x + 3y = 6) AND inside the red box.
    ttp://postimg.org/image/dev1vlexx/" target="_blank">

    As you can see by the two blue points below, it's possible to have a point in Region R, and it's possible to have a point not in Region R
    ttp://postimg.org/image/xxpy0nsv9/" target="_blank">

    Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

    Answer = E

    Cheers,
    Brent

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    Post Fri Aug 23, 2013 10:19 am
    Hi sana.noor,

    Here's a video explanation that I think you'll find helpful:

    Watch Rich CRUSH this DS question...

    GMAT assassins aren't born, they're made,.
    Rich

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