Land Your Score: Quantitative Reasoning Problems, Part 2

Welcome to “Land Your Score,” a blog series in which Kaplan instructor Jennifer Land shares key insights and strategies for improving your GMAT performance on Test Day. This week, Jennifer discusses how to solve Quantitative Reasoning problems using the Kaplan Method.

Solving Quantitative Reasoning GMAT problems

Last week, in the first part of our series, we used the Kaplan Method for Problem Solving to tackle this problem:

If x and y are both odd prime numbers and x < y, how many distinct positive integer factors does 2xy have?

1. 3
2. 4
3. 6
4. 8
5. 12

In that post we completed Steps 1 and 2 of the method, and we decided which approach to use in Step 3:

Step 1. Analyze the question.

Step 2. State the task.

Step 3. Approach strategically.

We are now ready to solve the problem using our chosen approach, picking numbers.

Picking numbers to find the answer

The basic rule for picking numbers is this: The numbers must be permissible and manageable. Let’s review the relevant information we gathered in Step 1:

• x and y are odd numbers
• x and y prime numbers
• x is less than y

So we know that the only permissible values for our variables are odd, prime numbers, where x is less than y. The most manageable options are the smallest odd prime numbers, so let x=3 and y=5.

Now that we have our numbers, we need to plug them into the expression in the question stem: 2xy = 2(3)(5) = 2(15) = 30. All we need to do now is to look for 30 in the answer choices and we are done!

Checking your answer

Wait! I forgot to use the all-important Step 4, a step I might have overlooked if 30 had been an answer choice. Always perform Step 4:

Step 4. Confirm your answer.

Part of confirming your answer is making sure the answer makes sense; in a problem asking for a sale price, the correct answer must be lower than the original price. The most important aspect to confirm about your answer is that you answered the right question. In this question, we were asked to count the factors of 2xy, so the number of distinct positive integer factors is what we need.

Finding positive integer factors

By plugging in 3 and 5, we solved the equation to find 2xy = 30. Let’s use that value to correctly answer this question. How many distinct positive integer factors does 30 have? To find out, we can make a simple factor tree. That’s the best way to make sure you do not omit any factors; the tree lets you account for all of them.

	30
1		30
2		15
3		10
5		6

Now that we have listed all of the pairs of positive integer factors for 30, all we need to do is count how many different factors are in the list! You can be confident you’ve listed all factors once you “meet in the middle.” When we got to 5 and 6 as a factor pair, the two columns had “met” so we knew we were done!

As this factor tree plainly shows, 30 has 4 pairs of different positive integer factors, making 8 the correct answer.

In the next installment of “Land Your Score,” I will take you back to Verbal Reasoning on the GMAT. We will walk through a Sentence Correction problem, identifying common flaws and how to correct them.

Want to master the Kaplan Method to earning a higher Quantitative Reasoning GMAT score? Visit Kaptest.com/gmat to explore our course options.

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