Determining How Much Time to Spend on GMAT Quant Questions

On the GMAT, you will be asked to answer multiple questions in a relatively short period of time. One of the main difficulties test takers have with the GMAT is that they run out of time before finishing all the questions. For the quant section, there are 37 questions to solve in 75 minutes, which gives an average of just over two minutes per question. Since you don’t want to finish at the 74:59 mark (unless you’re MacGyver), you can figure two minutes per question as a good target. The good news is that most questions can easily be solved within a two minute timeframe. Unfortunately, many test takers spend three or four minutes on questions because they do not understand what they are trying to solve.

One important thing to remember is that you won’t have a calculator on the exam, so blindly executing mathematical equations will be an exercise in futility. If the numbers seem large, the first thing to do is to determine whether the large numbers are required or just there to intimidate you. The difference between 15^2 and 15^22 is staggering, and yet most GMAT questions could use these two numbers interchangeably (think unit digit or factors).

Once you determine whether the bloated numbers truly matter, you need to ascertain how much actual work is required. If the question is asking you for something fairly specific, then you might need to actually compute the math, but if it’s a general or approximate number, you can often eyeball it (like proofreading at Arthur Andersen). Even if you end up having to execute calculations, you can usually estimate the correct answer and then scan the answer choices. Even in data sufficiency, determining how precise the calculations need to be can save you a lot of time and aggravation.

Let’s take a look at a question that can be somewhat daunting because of the numbers involved, but is rather simple if we correctly determine what needs to be done:

If 1,500 is the multiple of 100 that is closest to X and 2,500 is the multiple of 100 closest to Y, then which multiple of 100 is closest to X + Y?

(1) X < 1,500

(2) Y < 2,500

(A)   Statement 1 alone is sufficient but statement 2 alone is not sufficient to answer the question asked.

(B)   Statement 2 alone is sufficient but statement 1 alone is not sufficient to answer the question asked.

(C)   Both statements 1 and 2 together are sufficient to answer the question but neither statement is sufficient alone.

(D)   Each statement alone is sufficient to answer the question.

(E)    Statements 1 and 2 are not sufficient to answer the question asked and additional data is needed to answer the statements.

The first step here is to try and understand what the question is asking. It can be a little confusing so you might have to read it more than once to correctly paraphrase it. Essentially some number X exists and some number Y exists, and the question is asking us what X + Y would be. The only information we get about X is that 1,500 is the closest multiple of 100 to it, meaning that X essentially lies somewhere between 1,450 and 1,550. Any other number would lead to a different number being the closest multiple of 100 to it. Number Y is similar, but offset by 1,000. It must lie between 2,450 and 2,550. At this point we may note that the problem would be exactly the same with 100 and 200 instead of 1,500 and 2,500, so the magnitude of the numbers is simply meant to daunt the reader.

Without even looking at the two statements, let’s see what we can determine from this problem: Essentially if we add X and Y together, the smallest amount we could get is (1,450 + 2,450 =) 3,900.  The largest number we could get is (1,550 + 2,550 =) 4,100. The sum can be anywhere from 3,900 to 4,100, and therefore the closest multiple of 100 could be 3,900, 4,000 or 4,100, depending on the exact values of X and Y. This tells us that we have insufficient information through zero statements, which isn’t particularly surprising, but it also sets the limits on what we need to know. There aren’t dozens of options; we’ve already narrowed the field down to three possibilities.

(1)    X < 1,500

Looking at statement 1, we can narrow down the scope of value X. Instead of 1,450 ? X ? 1,550, we can now limit it to 1,450 ? X < 1,500. This reduces the maximum value of X + Y from 4,100 to under 4,050. This statement alone has eliminated 4,100 as an option for the closest multiple of 100, but it still leaves two possibilities: 3,900 and 4,000. Statement 1 is thus insufficient.

(2)    Y < 2,500

Looking at statement 2 on its own, we now have an upper bound for Y, but not for X. This will end up exactly as the first statement did, as we can now limit the value of Y as 2,450 ? Y < 2,500. This is fairly clearly the same situation as statement 1, and we shouldn’t spend much time on it because we’ll clearly have to combine these statements next to see if that’s sufficient.

(1)    X < 1,500

(2)    Y < 2,500

Combining the two statements, we can see that the value of X is: 1,450 ? X < 1,500 and the value of Y is 2,450 ? Y < 2,500. If we tried to solve for X + Y, the value could be anywhere between 3,900 and 4,000 (exclusively), so 3,900 ? X+Y < 4,000. This still leaves us in limbo between two possible values. To illustrate, let’s pick X to be 1,460 and Y to be 2,460. Both satisfy all the given conditions and give a sum of 3,920, which is closest to 3,900. If we then picked X to be 1,490 and Y to be 2,490, we’d get a sum of 3,980. The second situation clearly gives 4,000 as the closest multiple. If we can solve the equation using valid arguments and yield two separate answers, we have to pick answer choice E.

These types of questions can be daunting because of the big numbers and the ambiguous wording, but the underlying material on these questions will never be something that can’t be solved in a matter of minutes. The difficulty often lies in determining how much work we really need to do to solve the question at hand. The old adage is that you get A for effort, but that’s applicable when you tried earnestly and failed. On the GMAT, you want to put in as much effort as is needed, but the only A you want to get is for Awesome GMAT Score (admittedly an AGMATS acronym).

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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.