# When to NOT answer a PGRE question.

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1. Jul 24, 2013

### teroenza

Hello. I have a quick procedural question about the physics GRE. I know that incorrect answers deduct 1/4 point from your raw score, but I do not understand how questions that are left unanswered affect you.

Basically I am trying to understand if I have absolutely no idea how to answer a question, whether or not I should guess, or leave it blank.

Thank you

2. Jul 24, 2013

### TMFKAN64

Statistically, if you know *nothing* about a question, guessing will cost you as many points as you gain. (Guess 5 times, hit once, 1 - 4 * 1/4 = 0.) However, if you can eliminate an answer or two, guessing will help you. (If you can eliminate one answer, you'll hit 1 in 4 by guessing, and so 1 - 3 * 1/4 = 1/4.)

If you know absolutely nothing, Dirty Harry has the answer... "Do you feel lucky?"

3. Jul 24, 2013

### Staff: Mentor

For the expectation value: If you can exclude some value, or at least think that one answer is more likely than another: guess.
Guessing will increase the spread of your expected result - that can be positive or negative, depending on the result you want, and the number of correct answers you find.

4. Jul 24, 2013

### teroenza

Thank you both. I think I am confused about the penalty for leaving something blank. I'm used to the standard test where any attempt at an answer is better than a blank, so I don't understand why leaving a question blank would ever be advantageous on the PGRE.

5. Jul 24, 2013

### TMFKAN64

There is no penalty for leaving something blank.

Statistics says that if you guess at 5 questions with 5 possible answers, you should expect one right on average. However, if you are just guessing randomly, there is a 32.768% chance you'll get them all wrong, and lose 1 1/4 points.

So... do you feel lucky... punk?

6. Jul 24, 2013

### teroenza

This is a stupid question, but I have to ask it. What stops me from answering only one question, that I am absolutely confidant in getting right? Somehow this can't be allowed to happen, so would this process be penalized when the scaled score is computed?

7. Jul 24, 2013

### micromass

Staff Emeritus
You would get a 1% score. That doesn't seem very good...

8. Jul 24, 2013

### HallsofIvy

Staff Emeritus
No one is saying you are graded only on the questions you answer. What they are saying is that you get, say, 1 point if you answer correctly, 0 is you do not answer, and -1/4 point if you answer incorrectly.

If there are 100 question, you answer only one correctly, you get get 1 point, the "1%" micromass gives. If you answer that one question correctly, answer the other 99 completely at random, you would expect to get 99/5= 19.4, which I will round down to 19, correct and 80 incorrect Since you got a total of 20 right and 80 wrong, you will get 20-(1/4)(80)= 0 points.

9. Jul 24, 2013

### teroenza

Thank you very much HallsofIvy.