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# Is quadrilateral ABCD a rectangle? (A top left clockwise to

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26 Oct 2005, 07:41
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Is quadrilateral ABCD a rectangle? (A top left clockwise to D)

1. The area of triangle ABD is 1/2 the area of ABCD
2. The area of triangle ABC is 1/2 the area of ABCD
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26 Oct 2005, 08:33
E. You are missing information on one of the sides, which could result in it not being a rectangle. (The two triangle areas overlap, so 1/2+1/2 does not equal the whole area of the figure)
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Re: DS Kaplan Math Book Test 1 #23 [#permalink]

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26 Oct 2005, 10:25
GMATT73 wrote:
Is quadrilateral ABCD a rectangle? (A top left clockwise to D)

1. The area of triangle ABD is 1/2 the area of ABCD
2. The area of triangle ABC is 1/2 the area of ABCD

A case of ABCD like my illustration demonstrates why ABCD is not nescessarily a rectangle.
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26 Oct 2005, 11:39
I got an <b>E</b> without doing too much work on this. Using logic and a visual, I think it is entirely possible to have the 2 triangles overlap and as xennie mentioned, the areas will not equal the total area of the quad. We need more information.
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Re: DS Kaplan Math Book Test 1 #23 [#permalink]

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26 Oct 2005, 13:36
GMATT73 wrote:
Is quadrilateral ABCD a rectangle? (A top left clockwise to D)

1. The area of triangle ABD is 1/2 the area of ABCD
2. The area of triangle ABC is 1/2 the area of ABCD

A paralellogram for sure.

But a parallelogram is not recatngle unless the angles are at 90.

So E.
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26 Oct 2005, 16:07
E for me too.

Stmt's 1 and 2 alone aren't sufficient => CE
Stmts taken together might mean its a RECTANGLE or a PARALLELOGRAM or RHOMBUS, etc..
NOT SUFF => E
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26 Oct 2005, 18:52
Yep, OA is E. The sides must be at 90 degrees to be a rectangle.
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27 Oct 2005, 08:06
Yep - it appears that the GMAT likes to trick you into thinking quadrilaterals are rectangles, squares, rhombuses, etc. Some things to remember:

<b>Parallelogram:</b> Opposite sides are equal

<b>Rectangle:</b> All angles are 90 degrees & opposite sides are equal

<b>Rhombus:</b> All sides are equal & opposite angles are equal

<b>Square:</b> All angles are 90 degrees & all sides are equal

<b>Trapezoid:</b> One pair of opposite sides is parallel
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27 Oct 2005, 08:10
ValleyBall1 wrote:
Yep - it appears that the GMAT likes to trick you into thinking quadrilaterals are rectangles, squares, rhombuses, etc. Some things to remember:

<b>Parallelogram:</b> Opposite sides are equal

<b>Rectangle:</b> All angles are 90 degrees & opposite sides are equal

<b>Rhombus:</b> All sides are equal & opposite angles are equal

<b>Square:</b> All angles are 90 degrees & all sides are equal

<b>Trapezoid:</b> One pair of opposite sides is parallel

Thank you for providing those jargons!!
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27 Oct 2005, 08:33
Great information Valleyball! This is exactly the terminology we need to be familiar with.
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27 Oct 2005, 08:34
No problem! Now we just need to memorize them so we'll be able to quickly identify a GMAT trick question (especially in DS).
27 Oct 2005, 08:34
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