Guessing on SAT II Physics

Some students feel that guessing is like cheating—that guessing correctly means getting credit where none is due. But instead of looking at guessing as an attempt to gain undeserved points, you should look at it as a form of partial credit. Suppose you’re stumped on the question we looked at earlier regarding the charged particle moving in circular motion in a magnetic field. Though you don’t know the correct answer, you may know the answer isn’t the ideal gas law, because the question doesn’t deal with gases in any way. Suppose you also know that the answer isn’t Hooke’s Law, because Hooke’s Law deals with force exerted by a spring, and there are no springs in this question. Don’t you deserve something for that extra knowledge?

Well, you do get something: when you look at this question, you can throw out C and D as answer choices, leaving you with a one in three chance of getting the question right if you guess. Your extra knowledge gives you better odds of getting this question right, exactly as extra knowledge should.

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ETS doesn’t take off 1 /4 of a point for each wrong answer in order to punish you for guessing. They do it so as not to reward you for blind guessing. Suppose that, without looking at the questions at all, you just randomly entered responses in the first 20 spaces on your answer sheet. Because there’s a 20% chance of guessing correctly on any given question, odds are you would guess right for four questions and wrong for 16 questions.

You would be no better off and no worse off than if you’d left those twenty spaces blank. Now suppose in each of the first 20 questions you are able to eliminate just one possible answer choice, so that you guess with a 25% chance of being right. Odds are, you’d get five questions right and 15 questions wrong.

The lesson to be learned here is that blind guessing doesn’t help, but educated guessing does. If you can eliminate even one of the five possible answer choices, you should guess.