How to Do Math on the GMAT Without Actually Doing Math

On the GMAT quantitative section, the exam is testing your logic and analytical skills using mathematics as a medium. The topics used include geometry, algebra and arithmetic, all concepts that have been covered in high school curriculums around the world. However, the emphasis is really on the logic more than the math. In short, the question is simply asking you to solve a given problem by any means at your disposal. As such, many questions can be solved without doing any math whatsoever.

I often tell my students this quote: “The better you are at math, the less math you do.” This seems counter-intuitive at first. Lebron James is very good at basketball, and he plays a lot of basketball (when he’s not choosing cities to play in). It is reasonable to assume that proficiency in something makes you more likely to want to do it. However, on the GMAT, simply understanding what will happen is often enough to answer the question. The math can be used to confirm your thought, but it is not necessary and often will just slow you down.

A simple example would be to answer the question: “At a red light, there are 4 cars in 3 lanes. Is there at least one lane that has at least 2 cars?” The answer must be yes (by the pigeonhole principle, actually), because you have more cars than lanes. You don’t have to actually try the combinations to know the answer, but if you wanted to, you could imagine scenarios of the cars all in one lane, in two lanes, or in all three lanes. The math skills required to try every combination aren’t actually needed to solve a question like this, only an understanding of the permutation rules.

Despite many people swearing that the math on the GMAT is very hard, it’s often more a question of understanding than of math skills. Let’s look at an example that highlights this type of question:

Submarine A and Submarine B are equipped with sonar devices that can operate within a 3,000 yard range. Submarine A remains in place while Submarine B moves 2,400 yards south from Submarine A. Submarine B then changes course and moves due east, stopping at the maximum range of the sonar devices. In which of the following directions can Submarine B continue to move and still be within the sonar range of Submarine A?
I. North
II. South
III. West

A) I only
B) II only
C) I and II only
D) II and III only
E) I and III only

The submarines have a 3,000 yard sonar range in all directions, which essentially makes a circle around the ship. Submarine B moves a certain number of yards south and then a certain number of yards east. The question then asks which direction the sub could move in without losing contact.

This seems like a geometry question, and there are some numbers provided in this question. Let’s look through it quickly for the sake of completion, but you may have already noticed they won’t help in any meaningful way and are only there to bait you into tedious calculations. If submarine A has a circular range of 3,000 yards and submarine B moves south for 2,400 yards and then east, how far will it go east? The answer is actually a triangle inscribed within a circle, something like the figure below.

Given that submarine B ends up at the edge of the 3,000 yard range, the hypotenuse of the triangle is 3,000 yards, and the y-axis is 2,400 yards. The x-axis displacement is easy to calculate if you recognize this pattern as a glorified 3-4-5 triangle. Multiply those values by 600 and you get an 1,800-2,400-3,000 right triangle. Thus the sub moved east by exactly 1,800 yards. However, this information won’t really be helpful in answering the question as we’re being asked for directions, not distances.

The graph may help clarify the issue, but you can solve it without even using the graph either. Clearly the sub on the edge of the triangle can head back west and be within sonar range. Similarly, it can travel due north and stay within range as well. The only two directions that are not allowed are east and south. The answer must this be I and III together, which is answer choice E (also Kanye West’s daughter).

While proficiency in mathematics is helpful on the GMAT (and in life in general), it is often not a necessary skill in solving “math” questions on the exam. Remember that the main goal is to test your reasoning skills and determine whether you can correctly solve problems. Being a business student isn’t about being an expert at math, but rather using the information provided to swiftly reach the correct conclusion. Oftentimes, the better you are at math, the less math you’ll actually end up using.

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Ron Awad is a GMAT instructor for Veritas Prep based in Montreal, bringing you weekly advice for success on your exam.  After graduating from McGill and receiving his MBA from Concordia, Ron started teaching GMAT prep and his Veritas Prep students have given him rave reviews ever since.

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