GMAT Tip of the Week: Six Foot, Seven Foot, 600-to-700

GMAT PrepAs Hip-Hop Month rolls along in the Veritas Prep GMAT Tip of the Week space, we’re once again struck by how Lil Wayne has seemingly adopted the full persona of the GMAT for many of his recent tracks. As we noted earlier this year, his hit Right Above It includes several hints almost directly quoted from a GMAT test-writer, and if you listen closely Weezy is doing more of the same in his current radio single 6 Foot 7 Foot. As always, Weezy rhymes with the kind of insider knowledge of the GMAT that few outside of GMAC headquarters can even hope to have; could the title of his album “I Am Not a Human Being” really mean that the GMAT’s CAT is talking to us directly?

While Weezy deftly models the GMAT’s patented clever subtlety in one of the greatest “what? What does that even mean? Oh wait…that’s brilliant! That’s freaking brilliant!” lyrics of all time:

…real Gs move in silence like lasagna

He more directly offers you a GMAT tip with the first few bars of his second verse:

I’ve lost my mind

It’s somewhere out there stranded

I think you stand under me

if you don’t understand me

The wordplay is fantastic, of course, but the GMAT relevance is uncanny. In the first two lines, Weezy gets inside your head as a GMAT testtaker. Who among us hasn’t been in that situation at least once or twice? Our minds draw a blank and we’re stranded without the ability to even put our marker on the noteboard… What do we do? Well, look at the next two lines, in which Wayne adopts the persona of a GMAT question. “Stand under me if you don’t understand me” is Weezy’s way of saying this — look at the answer choices underneath the question if you read the question and are unsure of how to start. Often times, what stands under the question provides a pretty important clue to understanding the question itself, or at least to putting context behind your best method of solving it.

Standing under the question, as Wayne suggests, can include:

  • Scanning the answer choices of a Sentence Correction problems to see clear decision points between the options. If two choices use the past-tense and three use the present, that’s a decision point; if two use “its” and three use “their,” that’s a decision point. Often a quick glance at the answer choices can help you better gauge your next SC step.
  • Gauging the types of choices offered in a problem solving question can help you determine what type of process may be necessary. If algebraic answer choices, for example, all lack a denominator, you may need to work to multiply out all the fractions in the given information; if you see the square root of 3 in each answer choice, there’s a high likelihood that you’ll need to employ a 30-60-90 or equilateral triangle.
  • Checking the spread of the numbers in a problem solving question can help you to determine whether an estimate will suffice and help you avoid cumbersome calculations; similarly, noting the number properties of answer choices may help you to avoid math altogether.
  • Finding numbers that easily backsolve into a difficult equation can also help you to avoid messy algebra or calculation.

Consider the question:

A rectangular yard is 20 yards wide and 40 yards long. It is surrounded by a thick hedge that grows on the border of the property, but completely within the boundaries of the yard. If the hedge covers an area of 171 square yards, what is its width?

A) 160/120
B) 171/120
C) 180/120
D) 191/120
E) 800/120

To set this problem up, note that the difference between the exterior rectangle (the 20×40 rectangle) and the interior rectangle (inside the border) is 171. So we know that:

40*20 — (Area of interior) = 171

We can account for the area of the interior by recognizing that we’ll subtract the width of the border on all four sides. Accordingly, the new width is 20-2x and the new length is 40-2x (please note — we must subtract x twice from each side, since the border comes off of the top and bottom; the left and fright. Look at your computer monitor in front of you for a visual — the border is on all four sides!). That leaves us with the equation:

800 — (20-2x)(40-2x) = 171

You’ll likely recognize at this point that the math is about to get messy — in order to eliminate those parentheses, we’d need to multiply them out to form an involved quadratic. And unless you’re a huge fan of the Quadratic Formula (in which case, like Weezy, you are not a human being), you probably don’t want to do that. Which is why now is a good time to “stand under” the question for a second. If you look at the answer choices, two should stand out:

A) 160/120 reduces to 4/3
C) 180/120 reduces to 3/2

The others all turn into quite-awkward numbers, and since you’ll need to end up with a quadratic that provides an integer value (800 — 171 is 629), it’s quite unlikely that one of those messy fractions will do the trick. Accordingly, there’s a high likelihood that the answer will either be A or C, or that at worst having plugged one of those in will provide you with some insight as to whether you need a significantly larger or smaller border to provide this difference. As a savvy test-taker, you should notice that C provides you with both opportunities — it’s an easy plug-in, and it’s the median value so it can provide excellent insight even if it’s not correct. If you plug in C, you’ll also soon find another secret to finishing this problem quickly:

(20 — 2x)(40 — 2x) = 629

(20 — 2(3/2))(40 — 2(3/2)) = 629

NOTE: By using 3/2 we ensure that the 2 in front of each x will multiply out the denominator, leaving us with just integers. This looks promising since an integer answer is our goal. Were these to look inordinately messy even at this point we could reevaluate, but we’re on the right path here.

(20 — 3)(40-3) = 629

17 * 37 = 629

NOTE: We know we’ll get a unit’s digit of 9 now…it’s worth finishing off to be sure.

17*37 DOES in fact equal 629, so we know that C is the correct answer.

The key here is to know that the answer choices are part of the game. The GMAT can use them to tempt and trap you, but you can use them to frame your thinking and lighten your load. As a GMAT question might say to you directly, I think you should stand under me if you don’t understand me. If you need a hand starting or finishing a question, look to the answer choices below you and that can often provide the insight you need.

Wayne isn’t done dropping GMAT knowledge — he later in the same track starts to break down Sentence Correction, specifically, by saying that “I got through that sentence like a subject and a predicate” — so stay tuned to Hip Hop Month on the blog here each Friday. And, as always, be sure to find us on Facebook and follow us on Twitter!