GMAT Tip of the Week: Check Yo Self

GMAT Tip of the WeekWelcome back to Hip Hop Month in the GMAT tip space, where we’re consistently amazed at how often rappers take Veritas Prep’s advice and Think Like the Testmaker.  You’ve seen it from Weezy as he took on the persona of the number 0; from House of Pain as they adopted the mindset of the entire test itself; from Eminem as a geometry question…  Young emcees, including Young MC, seem to become one with the GMAT.  After all, when you really break it down the GMAT ain’t nothing but a G thang…

One of California’s finest, Ice Cube, is no exception to this rapper-as-test-author phenomenon (or maybe it’s just something like a phenomenon).  It’s as though his venomous, taunting lyrics in “Check Yo Self” are directed right at you from an arrogant testmaker’s perspective:

You better check yourself before you wreck yourself

Cuz I’m bad for your health, I come real stealth…

And then of course the chorus, which should echo in your mind like a steady drumbeat:

Chiggity check yourself before you wreck yourself

Chiggity check yourself before you wreck yourself

So chiggity check yourself  before you wriggity wreck yourself…

But while the lyrics may make it seem like Cube is taunting you, remember that the former gangbanger is also guilty of having a heart of gold and is now a mainstream family movie star.  He likes you; he’s just a big teddy bear in a White Sox cap and Raiders jacket.  And with these lyrics he’s sending you an important message about the GMAT.  Before you submit your answer to a problem solving question, you’d better check yourself before you wreck yourself. Why?  Because the GMAT comes real stealth.

Consider the question:

Andre purchased a stock for $120 two years ago.  In the first year, he earned a 20% return, and in the second year that value grew by 2/3.  Over the two year period, by what percentage did Andre’s investment grow?

(A) 66.67%

(B) 86.67%

(C) 100%

(D) 150%

(D) 200%

Doing the math, you’ll likely find that the $120 grows by 1/5 of itself the first year, and then by 2/3 of that new value the second year.  Accordingly, you could express the math as:

120 (6/5)(5/3)  —> 6/5 represents the original plus 1/5; 5/3 represents the new amount plus 2/3

Because the 5s in the numerator and denominator cancel, you’re left with 120 * 6/3 = 120*2 = 240.  Andre’s stock has doubled in value.  And because  the stock has doubled, you may look at 200%, see the prefix of ‘2’, and think you’re done.

But heed Ice Cube’s warning – chiggity check yourself before you wriggity wreck yourself here.  What does the question specifically ask for?  And what does 200% represent?

The question wants to know “by what percent did the value increase?”.  “Increase by” means “added to” – we want to know what percentage we added to the original value, not (as 200% represents) what we multiplied the original value by!  E is a trap answer designed to make the question look easy (an Eazy E?  Ice Cube and he parted company a long, long time ago).  But as Cube warns you, the GMAT “comes real stealth” like that – it knows the shortcuts you tend to make in the interest of saving time.  It’s not at all uncommon for you to see a number double and think “2-times” or “200%”, when really it’s just a 100% increase, added on to the 100% original value.  Be particularly careful with percentage problems, as nearly all percentage problems can be asked via this mechanism which allows for two “correct” answers based on whether they ask for “percent change” or “percent of”.

Percents were a main reason for the breakup of Ice Cube’s first successful music group, NWA (Cube felt he deserved – and rightfully so – a greater percentage of the group’s proceeds given the amount of music he wrote and produced), so perhaps that’s why he dropped this track to alert you to the specific dangers of percent problems.  But this logic applies to most GMAT problems, on which the most popular wrong answer is typically the right answer to the wrong question.  Before you submit an answer on the GMAT, Check Yo Self – make sure that you haven’t subconsciously skipped a step or made an assumption.  Do that effectively, and you can turn over the A-side of Ice Cube’s single “Check Yo Self” and listen to the B-side on your way home from the test center: It Was A Good Day.