Mia Saini: Hi and welcome to MBA PodTV. I’m your host, Mia Saini.

Today, we tackle a tricky data sufficiency problem on the GMAT with Manhattan GMAT’s Director of Product Development and GMAT guru Chris Ryan. So take out your notebooks and sharpen your pencils and get ready.

Chris Ryan: Hi! My name is Chris. I’m the Director of Product and Instructor Development here at Manhattan GMAT. After I graduated from Harvard with a Physics degree, I taught high school science for several years. Then I went back and got my MBA at Duke. After that, I worked at McKinsey for a couple of years then joined Manhattan GMAT where I’ve been teaching for over six years. Somewhere in there I got a 790 on the GMAT as well.

This is a data sufficiency problem in the low 600s range. Now, again on data sufficiency, the goal is to determine whether or not the statements give you enough information/sufficient data to answer the question definitively. Now, take some time with this problem. Pause the video, and when you’re ready, hit play.

Okay. So let’s start the problem up. Over here on the right by the way, we’ve got an image that says, “Your Paper.” This is meant to show you what your paper could look like. It’s not necessarily what your paper does or even should look like, but it gives you an idea of a paper-based process.

So what’s step one? Step one is process the question. So let’s look at the question again. Joe, Bob and Dad worked in the ratio of 1:2:4 hours respectively. How many hours did Bob work?

Now over on the right, we write down J, B and D with 1, 2 and 4 to represent their ratio of hours worked. We also note that Bob’s hours are the amount we’re looking for so we write B equals question mark.

Now at this point, many of you might move on to the statements, but what I’d suggest is that you try to rephrase the question further. If you look at the ration we have, it’s a three-way ratio. We have a ratio of three quantities. When we have a three-way ratio, we want to use a technique called the unknown multiplier.

Here is how it works. If you look at Joe’s time, right now we have 1 listed there, but we don’t really know how much time Joe works so let’s call it x. So if Joe worked x hours, how many hours did Bob work and did Dan work? Well, if the ratio is 1:2:4, then if Joe worked x hours, Bob worked 2x hours and Dan worked 4x hours. So we put those here. That means that what we’re looking for is 2x so we write 2x equals question mark. In fact, what we really want to know is what is x.

So what’s our next step? Well, step two is to pick the easier statement. That is, we look at the two statements and we quickly try to determine is one of the statements easier to start with; and if we can’t tell, just start with statement one.

Here, looking at the two statements, they look about the same in terms of difficulty. So we start with statement one and we also put down this answer grid, ADBCE, which corresponds to starting with statement one.

Now, what’s our next step? Of course it’s to process statement one. So looking at statement one again, we consider how can we put this down on paper? How can we make sense of it? Our key idea is to write an equation. So go ahead, take a moment now and try to write an equation based on statement one. Hit pause and when you’re ready, hit play again.

Ready? Your equation should look something like this: x plus 2x plus 4x equals 49. You might have started with J plus B plus D equals 49, but then you should substitute in the expressions involving the unknown multiplier x.

So is this sufficient? At this point, you might move on and actually work out the algebra, finding that 7x equals 49 and then x equals 7. But what would be great is if you can stop after writing that initial equation shown here in black and realize that’s sufficient, that’s enough information for you to find x.

So now we can use our answer grid. Cross out B, C and E and we’re left with just A and D as our possible answer choices.

So now, our last step is to process statement two. Here it is.

Take a moment and try to write another equation to represent statement two by itself. Go ahead and hit pause and hit play when you’re ready.

Ready? You should have written something like this: D equals J plus 21, or you might have gone directly to using x’s, in which case you would have 4x equals x plus 21. Again, at this point, you could continue with the algebra solving to find x, 3x equals 21 and then x equals 7, or you could stop at the black statements and realize that’s sufficient as well. You can solve for x. So our answer is D which represents the situation when each statement alone gives you enough information.

Before we close out this problem, I’d like to ask you how would you classify this problem? And of course one way we can classify this problem is as a ratios problem, specifically a three-way ratio using the unknown multiplier technique. We can also classify it as an algebraic translations problem because we needed algebraic translations techniques to turn the statements into equations.

And I’d like to also point out that it’s not a work problem. It doesn’t involve rates and amounts of work. It involves time, it involves work, but we don’t use rate times time equals work in this problem.

Mia Saini: Wow! Working on that GMAT problem gave me flashbacks when I took the GMAT five years go. So don’t put your notebooks away just yet. We have many more problem solving exercises from both the quantitative and verbal sections of the GMAT.

Well, that’s it for this edition of MBA PodTV. I’m your host, Mia Saini. Visit us at MBAPodcaster.com to get the latest video and audio shows. Also follow us on Facebook and Twitter to get the latest news and insight on your MBA application process.