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 Post subject: GMAT Geometry (Data Sufficiency)
PostPosted: Tue Jul 20, 2010 11:54 am 
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The lengths of three sides of a triangle are x, x + 2, and x + 4. What is the area of the triangle?

(1) The triangle is a right triangle.
(2) The lengths of two of the sides (in inches) are 8 and 10.

A. Statement (1) BY ITSELF is sufficient to answer the question, but statement (2) by itself is not.
B. Statement (2) BY ITSELF is sufficient to answer the question, but statement (1) by itself is not.
C. Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, even though NEITHER statement BY ITSELF is sufficient.
D. Either statement BY ITSELF is sufficient to answer the question.
E. Statements (1) and (2) TAKEN TOGETHER are NOT sufficient to answer the question, meaning that further information would be needed to answer the question.

(A) Statement (1) tells us that the Pythagorean theorem will hold for this triangle. x + 4 must be the length of the hypotenuse, since it is the largest number. Using the Pythagorean theorem, we can solve for x:
x² + (x + 2)² = (x + 4)²
x² + x² + 4x + 4 = x² + 8x + 16
x² = 4x + 12
x² – 4x – 12 = 0
(x + 2)(x – 6) = 0
x = 6 or -2.

We know that x cannot be negative, since the lengths of all sides must be positive. Therefore, x = 6 and the other sides of the triangle must be 8 and 10. So we can determine the area.
While it is not necessary to do so, we could calculate the area as follows:
Area = (1/2) × 6 × 8 = 24.

So Statement (1) is sufficient.

Statement (2) tells us the lengths of two sides, but we do not know the third. 8 and 10 can be either the two smaller or two larger sides, so the side lengths could either be 6, 8, and 10 or 8, 10, and 12. These two triangles have different areas. So Statement (2) is insufficient.

Since Statement (1) is sufficient and Statement (2) is insufficient, the correct answer is choice (A).\
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Hi, I think the answer for this should be D.
Statement (2) is also sufficient, if we know 8 and 10 are two sides then we find the third side using Pythagorean theorem we can't get 12 as an answer because it will contradict with premise given x, x+2 and x+4. If 8 and 10 are smaller side then hypotenus would be 12.81 hence not x + 4. only option is 6.


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 Post subject: Re: math (test 2, question 17): data sufficiency, geometry
PostPosted: Tue Jul 20, 2010 11:57 am 
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When we use statement (2) by itself we don't know if the triangle is a right triangle or not. So we can not use Pythagorean theorem in this case.


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 Post subject: Re: GMAT Geometry (Data Sufficiency)
PostPosted: Sun Oct 21, 2012 2:54 am 
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There is an error in explanation of Statement 2, : 8, 10 and 12 are not Pythagorean triplets.


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 Post subject: Re: GMAT Geometry (Data Sufficiency)
PostPosted: Sun Oct 21, 2012 2:56 am 
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Joined: Sun May 30, 2010 2:23 am
Posts: 498
questioner wrote:
There is an error in explanation of Statement 2, : 8, 10 and 12 are not Pythagorean triplets.
When we use Statement (2) alone we do not know if the triangle is a right triangle or not. Such information is given in Statement (1).

So when you consider Statement (2) after you have just considered Statement (1) remember to "forget" information from Statement (1).


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