What the White & Gold, Blue & Black, Periwinkle & Whatever Dress Can Teach You About the GMAT

Ron Point_GMAT TipsOver the past week, the online world has been consumed with discussions about one of the most mundane topics anyone could conceivably imagine. Indeed, for several days, the only discussion reasoned people seemed to be having was: “What color is this dress”?

Doctors, lawyers, engineers, (GMAT geeks), people of all walks of life were discussing the same basic concepts that toddlers learn in kindergarten. Is this dress blue and black, or white and gold? It seems preposterous even as I type it out, and yet people entrenched themselves into one camp or another with such certainty and vitriol that it seemed the other faction must be comprised of color blind philistines. Reportedly, some people saw the same picture differently in the morning and at night. Indeed, what was happening is that people were seeing the same thing from different perspectives.

People habitually see the same thing and reach different conclusions. If the middle-aged man next door buys a new sports car, some people assume he got a big raise, while others attribute it to a midlife crisis.  Other people might surmise he’s trying to impress someone new or perhaps he inherited a significant windfall. While seeing things from different perspectives is normal in everyday life, it is rare for multiple people to see the same thing and describe it completely differently. If I showed you the new red sports car, you wouldn’t likely tell me it’s a green bicycle or a blue toaster. At some point very early in our lives, we learn to associate certain words with certain elements, be they nouns, adjectives or colors.

Colors are such a fundamental part of life because so many things depend on them. We go on green lights, we stop for yellow school buses, we wear dark colors to appear more professional, and we wear our favorite team’s colors to show our support. Disagreeing about colors seems as basic as disagreeing that 2+2=4 (or 5 if you’re Orwellian). However the same thing can be seen from many different perspectives, and the variable is simply who is actually observing the phenomenon.

This happens a lot on the GMAT, and I wanted to discuss a problem that many people see one way, but others see in a completely different way:

The number of baseball cards that John and Bill had was in the ratio of 7:3. After John gave Bill 15 of his baseball cards, the ratio of the number of baseball cards that John had to the number that Bill had was 3:2. After the gift, John had how many more baseball cards than Bill?

  • 15
  • 30
  • 45
  • 60
  • 90

The way most people would look at this problem is that it’s an algebra problem. The ratio of two numbers is 7:3, and after an exchange of 15 cards, the ratio is now 3:2. I can set up two equations and solve for the two unknowns in this equation, which will give me the number of cards Bill has and the number of cards John has. After that, it’s simply a question of subtracting the two in order to answer the question. Let’s run through the algebra because it’s somewhat time-consuming but otherwise fairly basic (the white-and-gold approach).

The initial ratio, before the gift, can be describes as J / B = 7 / 3.

The final ratio, after the gift, would then be J – 15 / B + 15 = 3 / 2.

Note that we are defining J and B to be the initial values of John and Bill, so we’ll have to keep that in mind for the final calculation.

Cross-multiplying the first equation gives us 3 J = 7 B. This should make sense as John has many more cards than Bill.

Cross-multiplying the second equation gives 2 (J – 15) = 3 (B + 15),

We can expand this to 2J – 30 = 3B + 45.

Finally we can move the constants to one side and get 2 J = 3 B + 75

You can use either the elimination method or the substitution method to solve for the two variables. I prefer the elimination method so I’d multiply the first equation by 2 and the second equation by 3 to isolate J.

6 J = 14 B

6 J = 9 B + 225

Since the left hand sides are the same, we can simplify to 14 B = 9 B + 225.

Subtracting 9 B from both sides gives 5 B = 225.

Dividing 225 by 5 gives 45.

If B is 45, and 3 J = 7 B, then 3 J must be 315, and so J is equal to 105.

We’re still not done, because these are the initial values: 105 and 45. If John gave Bill 15 cards, then the new totals would be 90 for John and 60 for Bill, which is where the 3/2 ratio comes in. The difference in cards is 30 after the gift, so the answer is B.

Other people see this ratio problem and don’t even think about the algebra, they solve it using the underlying concept (the blue-and-black approach). To illustrate this concept, suppose I had 199 cards and you had 101 cards. Since no simplification is possible, the ratio of our cards would be 199:101. But if you then gave me one card, our ratio would suddenly be 2:1. This reduced fraction does not change the fact that I still have 200 cards and you have 100. Simply because the fraction can be simplified, that does not mean that the totals have changed in any way.

Let’s apply that same logic here. The ratio was 7:3. After the gift, the new ratio is 3:2, but the total number of cards has stayed the same. This means that if I can get a new ratio that’s in the same proportions as the old ratio, the problem will seem much simpler. The ratio 7:3 has 10 total parts. The ratio of 3:2 has only 5 total parts, so they are not in the same proportions. However, if I recognize that I can simply multiply 3:2 by 2 to get a ratio of 6:4, I discover a shortcut that can help on ratio problems.

If the ratio used to be 7:3 then became 6:4 after a transfer of 15 cards, then each unit of the ratio must represent 15 cards. This would mean that 7 would drop to 6 and 3 would increase to 4 because of the same 15 card transfer. Thus the old ratio was (7×15): (3×15), or 105:45. The new ratio is similarly (6×15): (4×15), or 90:60.  The difference in cards after the gift is still 30, answer choice B, but for some it’s much easier to see using a little logic than a lot of algebra.

On the GMAT, similar to the chameleon dress, your perspective is what’s going to dictate how you approach problems. Not every question will have a shortcut or an instant solution, but every problem can be approached in multiple ways. The only limit is your understanding of the concepts and your skill at analyzing the presented problem. Hopefully, on test day, these strategies will help you avoid feeling blue (and black).

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Ron Awad is a GMAT instructor for Veritas Prep based in Montreal, bringing you weekly advice for success on your exam.  After graduating from McGill and receiving his MBA from Concordia, Ron started teaching GMAT prep and his Veritas Prep students have given him rave reviews ever since.