Learn to Love Data Sufficiency When You Hate Math

I often have students who, in the first few weeks of the GMAT course, tell me they really can’t stand Data Sufficiency. They fall into a few different camps, but we’ll look at two primary ones.

First, we have our engineers and “number crunchers,” frustrated by Data Sufficiency because there’s no closure, so to speak, at the end. There’s truly something rewarding for a lot of us about grinding out a page of math and getting to an answer.

However, not only does the GMAT fail to reward you for that – it will actually penalize you for spending too much time reaching an answer.  These students have to be retrained and look for a different kind of closure.

Let’s come back to this.

The other camp of students consists of those who genuinely don’t like math. They particularly don’t like GMAT math, and the Data Sufficiency section seems plain weird. There’s no solution-orientation, or at least not one with which they’re familiar, and the whole process is odd and frustrating.  This is the camp that can really learn to revel in Data Sufficiency.

There are a few things to realize. Data Sufficiency is FANTASTIC for those of us who are lazy about math. We do a few calculations, write down a few equations, and then the magic of this section is that we can look at it and say, “Yeah, I could totally finish that if I wanted to.” (Or as one student said, “I could totally finish this if I were much better at math than I am.”) Either reaction is fine – but the bonus is that you get to walk away from the problem at that point! How often do you get to start something, work half way through it, and then walk away and get full credit? Voila!

Our engineers (and other math people) have to think of this a different way. Let’s make a golf comparison here. When I play golf with my mom, and the ball ends up within about a foot of the hole, she’ll call a “gimme” and pick up the ball, and move on to the next hole. Because she’s my mom, I don’t remind her that there’s still a good chance it would have missed the hole. Data sufficiency is like that. As long as you’re within putting distance of the hole, it’s “good enough” and you can walk away and move on to the next question.

We get to the point where we see the end of the problem, or we see where we could take it, if we had an extra 45 seconds, or 2 minutes, or even 15 minutes and a calculator, and we call a “gimme” and move on. No bonus points for finishing the work – just for seeing that it can be done.

Yes, it’s a weird section. Yes, it can be frustrating. Think of it as a game, though – and a game where you don’t actually have to cross the finish line; you just have to spot the finish line in the distance, and it’s good enough.

Let’s look at a problem that both camps would dislike:

If x>0, what is the value of x?

(1)  x^2 = 21904

(2)  x is an integer, and the approximate square root of x is 12.1655

In this case, either statement is sufficient. We know that if we wanted to, we could find the square root of that big ugly number, and we know that if we wanted to, we could also square 12.1655 and get to something. In either case, we shouldn’t even begin the work. We just recognize that it can be done, and we select D and move on.

How about another one from the homework:

The surface area of a rectangular field was changed so that the length of one of the dimensions was reduced by 10 feet and the length of the other dimension was increased by 20 feet. What was the surface area before these changes were made?

(1) After the changes were made, the surface area was 2,500 square feet.

(2) The length and width of the field were equal after the changes were made.

Ok – looking at the question, we have a couple of equations:

LW = old surface area

(L-10)(W+20) = new surface area

We are asked to find LW

Statement 1 gives us (L-10)(W+20) = 2500

On its own, we know this isn’t sufficient, because we have a single equation and 2 variables, and when we multiply these together, we have some L terms and some W terms and some LW terms. There’s no way we’re going to be able to separate all these pieces and get just LW.  Statement 1 is insufficient. No need to take this through any additional steps.

Statement 2 gives us L-10 = W+20

This is helpful, but not enough – the problem is that we still don’t have any metrics, with this statement alone, to tell us how big the field is. It might be 100 square miles, or it might be 100 square feet. Insufficient on its own.

Together:

(L-10)(W+20) = 2500

L-10 = W+20

Now, with both of these, we have two variables and two equations, and the two equations are distinctly different. This means we have enough. Not convinced?

Use the second equation, and we can express L in terms of W or vice versa. Then plug that back into the first one, and we’d have an equation with just one variable. We can solve this. That gives us a number for one variable, and we can use either equation to find the other one. Don’t do the math; don’t multiply this out through five steps. Just see that we can get it down to a single variable and a single equation, and trust that, given some time, you could solve the algebra. Now pick C and walk away. From this point, it’s a “gimme” question.

They’re not always this simple – but the key is to know when to stop calculating and walk away. It’ll shave time off of MANY questions, which is always a bonus for those questions when you really need those extra few seconds.

Plan on taking the GMAT soon? We have GMAT prep courses starting all the time. And, be sure to find us on Facebook and Google+, and follow us on Twitter!

Valerie Browning has been teaching GMAT for Veritas Prep for 10 years. After graduating from the McCombs School of Business at UT Austin, Valerie is now based in Houston. Since graduating, she has been interviewing applicants to McCombs as an alumni volunteer.

2 Responses

  1. Vaishno says:

    What is the value of x?
    (1) x^2 = 21904

    Doesn’t statement 1 mean x has two values + and -? So we cannot get one value of x therefore statement 1 is not sufficient.

  2. Valerie Browning says:

    Vaishno,
    You’re exactly right!! I should have changed the question to read, “If x>0, what is the value of x?”
    Thanks for catching this for me,
    Valerie

Leave a Reply

Spam protection by WP Captcha-Free