Official Guide Explanation:
Data Sufficiency #19




This is just one of hundreds of free explanations I've created to the quantitative questions in The Official Guide for GMAT Quantitative Review (2nd ed.). Click the links on the question number, difficulty level, and categories to find explanations for other problems.

These are the same explanations that are featured in my "Guides to the Official Guide" PDF booklets. However, because of the limitations of HTML and cross-browser compatibility, some mathematical concepts, such as fractions and roots, do not display as clearly online.

Click here for an example of the PDF booklets. Click here to purchase a PDF copy.


Solution and Metadata

Question: 19
Page: 154
Difficulty: 4 (Moderately Easy)
Category 1: Geometry > Triangles > Pythag

Explanation: If a2 + b2 = c2 (the pythagorean theorem), the triangle is a right triangle; the angle opposite side c would be the right angle. Statement (1) is sufficient: if x + y = 90, the remaining degree measure for the third angle is 180 - 90 = 90, so that angle is a right angle. Statement (2) is insufficient: if x = y, the triangle is isoceles, but there's no proof that it has a right angle--for instance, if x and y equal 40 degrees, then the third angle would be 180 - 40 - 40 = 100. Choice (A) is correct.

Click here for the full list of GMAT Quant Review explanations.


You should follow me on Twitter. While you're at it, take a moment to subscribe to GMAT Hacks via RSS or Email.

Total GMAT Math

The comprehensive guide to the GMAT Quant section. It's "far and away the best study material available," including over 300 realistic practice questions and more than 500 exercises!
Click to read more.