Hi,

It could be bad. You could lose 20-30 points.

You have to guess. Getting something wrong penalizes you less than unattended questions.

GMAC has released some information about this and basically, if it is a couple of questions at the end of the Quant it may be not make much a difference if you fail to answer or if you guess incorrectly.

However, you have hinted at the correct strategy earlier in your posting. You see, if you get to the last few questions (say 5 to 7) and you are completely out of time then either way - guessing or leaving blank - you have failed one of the major tests of the GMAT: time management.

It is better for you to leave behind questions along the way that you have little chance of getting right. I have had tutoring students take the GMAT Prep and have to guess at the last several questions due to time. They nearly weep when they see that they guessed at questions that they would absolutely have gotten right. So be proactive as you practice your timing.