Sarlin vs. Evil. Bet Sarlin.

Our post this week comes from Alex Sarlin, Verbal Lead at Knewton, where he helps students with their SAT prep.

If you’ve begun your SAT prep, you’ve probably already realized that the test-makers aren’t exactly mild-mannered or kind—quite the opposite. Luckily, we at Knewton have their number. Today we’ll be revealing one of their signature tricks.

First, a quick aside. Have you ever heard this old word-game? It goes something like this:

You: Let’s play a game. I’m bet I can get you to say the word “black.”

Friend (smirking): No way.

You:  OK. Name the colors in a traffic light.

Friend (thinking, suspicious): Red… yellow… green.

You: How about the colors in the American flag?

Friend: Uhh… red… white… blue.

You: Gotcha! Oh man, that was so easy!

Friend (surprised): What?!

You: I made you say blue. You totally weren’t even paying attention.

Friend: What?! You said you were going to make me say ‘black!’

You: NOW I gotcha.

So very evil. And there’s a moral, too: Never let your guard down before the game is over.

The SAT writers use their own version of this trick on the math section of the test. They give you a rather complex problem, and then, just when you’re at the very last leg of your problem-solving, they’ll offer you an answer choice that refers to the next-to-last step. After all that work, many test-takers cling to this number like a life preserver, forgetting to do that last, important step and completely wasting all the time they just spent.

Let’s look at some examples:

8. There are 2 different ways to arrange the 2 letters A and B in a row from left to right. How many more different ways are there to arrange the 5 letters A, B, C, D and E in a row from left to right?

A.      60

B.      100

C.      118

D.      120

E.       625

Ah, permutations and combinations: everybody’s favorite subject. Dig into your math knowledge: you need to put the number of possibilities into “slots.” There are 5 possibilities for the first slot (A, B, C, D or E), 4 for the second (because one letter is gone), 3 for the next slot, and so on. You end up with 5 x 4 x 3 x 2 x 1 = 120 different combinations. Choice D. All set, right?

Wrong. The question actually asked how many more different ways are there to arrange 5 letters than there are to arrange 2 letters. Because there are 2 ways to arrange two letters, there are 118 more ways to arrange five letters. Choice C is correct—not evil Choice D.

Now try this problem, which has not one, but three evil answers lying in wait:

4. Hector is both the 4^th tallest and the 4^th shortest person in his family. If everyone in his family is a different height, how many people are in Hector’s family?

A.      6

B.      7

C.      8

D.      9

E.       10

Some test-takers will think, OK—four taller, four shorter, eight people, choice C, done. Those people obviously aren’t paying attention. For one thing, they forgot about Hector himself!

Others think, Ah ha! Four people taller and four shorter, plus Hector. There are nine people in Hector’s family: Choice D! That might sound like it makes sense—but it’s still wrong.

In reality, if Hector is the fourth tallest, then actually there are only three people taller than he is. He is the fourth tallest. The same goes the other way. There are three people shorter than he is. And, then, we have to add Hector. There are 7 people in Hector’s family. Choice B is correct.

As you can see, the SAT isn’t out to make friends. Watch out for answer choices that seem too obvious or simple to be correct—they often are. These are particularly evil examples, but in fact, the SAT uses this trick, in some form or another, on many math questions. Beware, and think twice before choosing the “obvious” answer!

Check out the Knewton blog for more Evil SAT Tricks!