An underutilized strategy for GMAT geometry questions

By Brent Hanneson - July 22, 2020

Put your exam hat on and play close attention to your thought process as you try answering the following question (posted on GMAT Club by Math Revolution) in 2 minutes:

Debrief question: If you weren’t able to answer the question, did you consider estimating the area of the shaded region? If you didn’t, you may be missing the opportunity to maximize your success rate with Geometry questions.

Many students forget that the geometric figures in GMAT Problem Solving questions are drawn to scale unless stated otherwise, which means we can use visual estimation to eliminate answer choices before guessing. In fact, with some questions, we can successfully eliminate 4 answer choices and quickly reach the correct answer without performing any complicated calculations. 

For the linked question above, the area of the square is 144. Since the shaded area appears to take up less than 50% of the square, we can eliminate answer choices D and E (75 and 90), since they’re more than half the square's area. Likewise, answer choice A (30) suggests that only about one-fifth of the square is shaded, and we can easily see that a lot more than one-fifth is shaded. So, we can eliminate A as well.

So, with some visual estimation, we're down to answer choices B and C. If you're especially good at mentally arranging shapes, you might even conclude that, since answer choice B (45) implies less than one-third of the area is shaded, we can eliminate that as well.

So, using the fact that the diagram is drawn to scale, we can quickly make a well-informed guess that requires no knowledge of Geometry.

That’s it!

Here are some questions to practice your estimation skills:





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