Guessing and the Math IC

　　Should you guess on SAT II Math IC? We'll answer this question by posing a question of our own:

　　G. O. Metry is holding five cards, numbered 1–5. Without telling you, he has selected one of the numbers as the “correct” card. If you pick a single card, what is the probability that you will choose the correct card?

　　One out of 5, or 1 5, of course! And that's precisely the situation you're in when you blindly guess the answer on any SAT II Math IC question: you have a 1 in 5 chance of getting the question right. If you were to guess on 10 questions, probability says you'll get two questions right and eight questions wrong. Two right answers earns you 2 raw points. Eight wrong answers gets you –2 raw points (8　– 1/4 points).　　Those ten answers, therefore, net you a total of 0 points. And that's exactly what ETS wants. They designed the test to make blind guessing pointless. 　　Educated Guessing　　But suppose you’re faced with this question:

　　If x + 2x = 6, what is the value of x?

　　(A)–2

　　(B)2

　　(C)3

　　(D)0

　　(E)1

　　Let's say you have no idea how to solve this problem. But you look at the answer choices, and realize that 0 multiplied by any number equals 0. If you plug that into the equation,　cannot add up to 6. You can eliminate “0” as a possible answer, and now have four choices from which to choose. Now is it worth it to guess? Yes. Probability states that if you are guessing between four choices you will get one question right for every three you get wrong. For that one correct answer, you'll get one point, and for the three incorrect answers, you'll lose a total of 3/4 of a point: 1 – 3/4 = 1/4. If you can eliminate even one answer, the odds of guessing turn in your favor: you become more likely to gain points than to lose points. 　　The rule for guessing on the Math IC test is simple: if you can eliminate even one answer-choice on a question, you should definitely guess