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GMAT Prep2 another geometry problem

Expert replies
by jaydeer44 » Mon Aug 25, 2008 5:39 pm
Can someone please explain this problem to me? I think I am misunderstanding it. The answer is E. I thought it was D...

For statement 1, if two of the angles are right angles, doesn't that mean that all four angles have to be right, and thus all angles = 90 degrees?

For statement 2, if there are a total of 360 degrees in a quadrilateral, and angle ABC is twice the degree measure of angle BCD, doesn't angle ABC have to = 120 degrees and angle BCD = 60 degrees? if not, can you please illustrate how so?

Thanks!
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Source: — Data Sufficiency |

strange

by jackcrystal » Mon Aug 25, 2008 6:05 pm
I think it should be A

whats wrong here? :shock:
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Re: GMAT Prep2 another geometry problem

by Ian Stewart » Mon Aug 25, 2008 6:21 pm
jaydeer44 wrote:Can someone please explain this problem to me? I think I am misunderstanding it. The answer is E. I thought it was D...

For statement 1, if two of the angles are right angles, doesn't that mean that all four angles have to be right, and thus all angles = 90 degrees?

For statement 2, if there are a total of 360 degrees in a quadrilateral, and angle ABC is twice the degree measure of angle BCD, doesn't angle ABC have to = 120 degrees and angle BCD = 60 degrees? if not, can you please illustrate how so?

Thanks!
This problem was recently discussed here:

www.beatthegmat.com/measure-of-interior ... 17001.html

To answer your questions, you can have any combination of angles in a quadrilateral, provided they add to 360. If you draw a rectangle, then erase the top of it and extend only one of the heights, then connect the topmost corners, you should get a shape with a base that looks like a rectangle, but with a 'sloping roof'. The angles can easily be made to be 90-90-45-135 in this way, which is how you can make a quadrilateral with two right angles, and with one angle that is double another (because 90 = 2*45), but which does not contain a 60 degree angle. Or you can have a parallelogram with 60-120-60-120 angles, so both statements together are not sufficient.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com
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by jaydeer44 » Mon Aug 25, 2008 7:45 pm
thanks! i definitely mixed up the definitions of quadrilateral and parallelogram and thus the confusion
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