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GMAT Tuesdays with Kevin: GMAT Quant Challenge Question

Hello! :) Today, I talk through how to solve this tricky-looking geometry question. If you have any questions for us or suggestions for future video topics, let us know in the comments below. Enjoy!

About the Author

Kevin has taught for over ten years from San Francisco to Japan, helping students prepare for tests, like the GRE, GMAT, and SAT. He enjoys sharing what he learned, so even more students can achieve their goals. When he is not helping students dominate standardized tests, you can find him in the Pacific Ocean or on a granite dome in the Sierra Nevada Mountains. Follow him on Google+ and on Twitter @KevinRocci!

4 Responses to GMAT Tuesdays with Kevin: GMAT Quant Challenge Question

  1. Shreya Motwani October 9, 2013 at 1:23 pm #

    Hello Kevin,
    I have a question/doubt regarding this problem. How can we be sure that the given figure is a square? The question does not say anything about AB II CD.

    • Kevin
      kevin October 9, 2013 at 1:48 pm #

      Hi Shreya, great question! You are right that we are not explicitly told that AB is parallel to CD. But we can figure this out a couple of ways:

      For one, we know the lengths of three sides of the shape. And since the sides are all the same length, and especially since AB and CD are the same length, I know that if I draw a line from A to D, it will be the same length as BC. If we have sides with all the same length, then we have a square.

      Second, and more importantly, I left out a crucial piece of information when I copied down the problem on the white board. Look at the original problem (http://gmat.magoosh.com/questions/104) and see if you can see what I left out. Do you see it? No really. Did you look? :)

      That’s right, B and C are right angles. As such, AB and CD are parallel. From there, we know that our lines are parallel, and we know they are the same length. Thus, we have made a square.

      I hope this helps! :)

  2. Rahul Sehgal October 9, 2013 at 10:54 am #

    This is a very good problem. One take away for me would be to make sure when the question says – perimeter, make sure I am bother ONLY about the length of the sides of the figure. :).

    This question was tricky.

    • Kevin
      kevin October 9, 2013 at 1:54 pm #

      Hi Rahul, I’m glad that you enjoyed this problem. It is a tricky one for sure, but kind of fun too. :)

      I definitely agree with you—always important to know what you are dealing with. Taking the time to properly evaluate the problem and pinpoint what you are dealing with will ultimately save you time. It’s way better to know what to do from the beginning instead of discovering it halfway through the problem and having to start over or never noticing it and choosing the wrong answer.

      I see a lot of students dive straight into math problems without coming up with a plan or evaluating all the information in front of them. Often they make assumptions about the problem and then attempt to solve it. This is not a winning strategy. Take the time to process all the information presented in a math problem.

      Good luck with the test prep and keep us posted on how it goes. :)


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