I think parenting should be about having fun instead of feeling frustrated.  If you have a child who likes to ask you silly questions or questions to which he or she already knows the answers, here are some responses you can use:

"That's a great question.  What do you think?"

Give the child a silly, illogical, off the wall response such as, "Maybe the birds were flying too low when they skipped over the barn this morning."  Then walk away while the child stops to figure out what you said.