How to answer a question?

I've been asked a question,
and I don't know the answer.
How can I avoid looking dumb?

BUY TIME. Restate the question. That gives you that extra moment to pull your thoughts together and come up with an answer.

ASK A QUESTION ABOUT THE SENSE OF THE QUESTION. Ask your questioner to rephrase.

DON'T ANSWER A QUESTION YOU CAN'T ANSWER WELL. An ill-conceived answer is worse than no answer.

IF YOU DON'T KNOW, ADMIT IT. Then set a time and date by which you will have the answer.

DELEGATE THE QUESTION. If someone is present who you think will have the information, pass the question to him.

SUGGEST ANOTHER PERSON OR RESOURCE THAT MIGHT HAVE THE ANSWER.

Source :  Maximize Your Presentation Skills / Ellen A. Kaye / Golden Books