GMAT Tip: Consider the Possibilities and Make a Well-Reasoned Guess
In the GMAT Quantitative section, there are often problems that appear simple but turn into big time-wasters that detract from test takers’ ability to get to the tougher questions and/or finish the quantitative section of the exam. These time-wasters are a) often arithmetic questions b) also data sufficiency questions and c) seem very simple from the outset.
The GMAT is testing your ability to manage your time, and a test taker with excellent time management skills recognizes that when you are at 85% of the way in solving a problem, often an educated guess (and likely correct) guess is more valuable than allowing precious seconds count down from the count.
The below data sufficiency question perfectly illustrates what we are referring to:
If x and y are integers and 2 < x < y, does y = 16?
(1) The greatest common factor of x and y is 2.
(2) The lowest common multiple of x and y is 48.
Thinking back to our decision tree, Statement (1) should relatively easy to evaluate. If the GCF of x and y is 2 and 2 < x < y, then the sky’s is the limit with what the answer should be.
That should let us to our evaluation of Statement (2). The LCM of x and y is 48 – let’s think of what the possibilities might look like. Well, if x = 3 and y = 16, then indeed, y would have to be 16, right?
The problem is that if x = 24 and if y = 48, then the LCM would also be 48. y is not necessarily 16 – there are other combinations that would provide Statement (2) true.
Many test takers are then going to jump quickly select (E) as their answer choice, only to uncover later than they are incorrect because the correct answer is (C). In many ways, this question is testing your ability to understand factors, but there are other ways to get to the right answer.
When assessing Statement (2) we could also conceptually realize we need a “limiting factor” to the pairs of x and y that share a LCM of 48. When provided several parameters – 2 < x < y and the GCM of x and y is 2, and the LCM of x and y is 48, shouldn’t that be enough limiting factors to determine whether either y is (or isn’t) equal to 16?
Likely, we just don’t have sufficient time to think through all of the possibilities where that would prove true to give us the exact pair of what x and y is for this question. But, this is a data sufficiency, and not a problem-solving question. For Statement (1) the possibilities are too endless, and while not quite as numerous as with Statement (1), Statement (2) proves to have the same problem. But combined, it is more likely to prove there is a concrete possibility to sway yes versus no than the likelihood that there is not sufficient information.
When tackling tough time-wasting questions like this one, just think of what is more likely the right answer, and then move on to apply your time to another question – if you have come up with a bunch of possibilities already, then consider what that means to the problem and select your best guess.
The above GMAT Tip comes from Veritas Prep. Since its founding in 2002, Veritas Prep has helped more than 100,000 students prepare for the GMAT and offers the most highly rated GMAT Prep course in the industry.