GMAT Tip of the Week: Spotting the Trap

Matt Damon’s character in the poker-themed movie Rounders had a famous line: “If you can’t spot the sucker in the first half-hour at the table, then you are the sucker.”  The same is often true of GMAT questions — on a difficult question, if you can’t spot the sucker choice, the most popular incorrect answer, there’s a high likelihood that you’ll pick it it yourself.

Learning to understand the GMAT’s popular “sucker choice”  techniques can make you a much better test-taker.  It can also be a much more enjoyable way to study — instead of seeing the traps as threats, you can learn to enjoy the process of outsmarting the GMAT authors.  It’s also a great way to learn from your mistakes, noting after you’ve reviewed an error “I see where you tricked me,” a knowing insight into the test and not a criticism of yourself.  The test is cleverly written, so embrace the insights you  gain about it.  Note a few things about trap answers on the GMAT:

- To be a truly well-written “sucker” choice it has to be satisfying to an examinee

- The trap answer generally answers a question, but not the question

- Trap answers usually leave the process a step short or include some partial correctness…but a fatal flaw

Let’s consider a couple examples:

Raisins are made by drying grapes in the sun. Although some of the sugar in the grapes is caramelized in the process, nothing is added. Moreover, the only thing removed from the grapes is the water that evaporates during the drying, and water contains no calories or nutrients. The fact that raisins contain more iron per food calorie than grapes do is thus puzzling.

Which one of the following, if true, most helps to explain why raisins contain more iron per calorie than do grapes?

A.Since grapes are bigger than raisins, it takes several bunches of grapes to provide the same amount of iron as a handful of raisins does.
B.Caramelized sugar cannot be digested, so its calories do not count toward the food calorie content of raisins.
C.The body can absorb iron and other nutrients more quickly from grapes than from raisins because of the relatively high water content of grapes.
D.Raisins, but not grapes, are available year-round, so many people get a greater share of their yearly iron intake from raisins than from grapes.
E.Raisins are often eaten in combination with other iron-containing foods, while grapes are usually eaten by themselves.

The most popular incorrect answer here is A.  Why?  Choice A answers the wrong question — but it does answer “a” question.  Choice A is true — and after reading some nutrition science information that may not seem a natural topic for many, many examinees are happy to see an answer choice that is clearly true and is easy to understand.  It’s satisfying to you — you can confidently say “I know A to be true.”  But look at the question stem — it even includes the qualifier “if true.” It doesn’t matter, for the purposes of this question, whether that statement is true..it simply must answer the question about the particular IRON/CALORIE ratio.  Which A does not (B, in fact, does).   Here you can see a common setup for a trap answer — it includes information that is clearly true, but does not answer the question.

The ratio of television sets to radios at an electronic store before a new shipment arrives is 12:7.   If no television sets or radios leave the store and the only television sets and radios that arrive are in the new shipment, what is the ratio of television sets to radios after the new shipment arrives?

(1)    The new shipment contains 132 television sets

(2)    The new shipment contains 77 radios

[DATA SUFFICIENCY ANSWER CHOICES APPLY]

Here, the trap answer is E.  Note that it’s “satisfying” for you to be able to recall about ratios that, when only given an initial ratio and then adding a particular number, you cannot tell the impact on the new ratio (were there 19 appliances to start, or 19,000?).  You can pat yourself on the back for knowing that about ratios, feel confident in your answer, and move on.  But you haven’t spotted the “sucker” — which is that there’s one exception: If the numbers that you add are in the same ratio as the original, the ratio remains unchanged.  And 132 TVs and 77 radios added is a ratio of 12:7 (each is a multiple of 11).  So the correct answer is C — we can prove with both statements together that the ratio remains at 12:7.

And here’s where the “spot the sucker” mentality can help you — that the answer is C probably does not present itself too clearly to anyone based on the numbers.  But if you know to suspect a trap, and choice E seems to come a bit too easy, you know that you should spend some time investigating further.   A common Data Sufficiency trap is for the test to give you an answer that comes with a little bit of satisfaction (“I know that rule!”) but that still doesn’t take much time or ingenuity to solve.  Know that low levels of satisfaction are highly correlated with trap answers — use that as your cue to investigate just a bit further.

Uncle Bruce is baking chocolate chip cookies.  He has 36 ounces of dough (with no chocolate) and 15 ounces of chocolate.  How many ounces of chocolate are left over if he uses all the dough but only wants the cookies to consist of 20% chocolate?

(A)                  3
(B)                   6
(C)                   7.2
(D)                  7.8
(E)                   9

Here the trap answer is E.  One can see the ratio of 4 parts dough (80%) and 1 part chocolate (20%) and note that, if the dough stays unchanged at 36 ounces, then the chocolate must be 9 ounces.  Which corresponds to E, and provides you with that satisfaction of “I solved it!” The phrase “oldest trick in the book” is used quite often, but on the GMAT this is probably it — the trap answer answers the wrong question, and the correct question requires most examinees to take one extra step with that intermediate number.  The satisfaction comes from arriving at a number after some algebraic work — and you see that number reflected in your answer choice.  Know that this is often a trap! 

Simply finding a number that matches an answer choice is not a guarantee of a correct answer… If you’re going to make a mistake, you’re often better off if your number does not match an answer choice, because at least you know you have to go back and fix something.  Always check that your number represents the quantity being requested.  And smile when you see the trap answers that less-savvy examinees will certainly pick.  If you’ve trained yourself to spot the sucker, you can successfully avoid many of the GMAT’s cleverly (but formulaically!) written traps.

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