Logic Riddles

Question: A farmer has 10 cows, all but six die. How many are left?

Question: Disgusting and small, we wriggle through your halls, devouring books, cloths and walls. Alone we are feeble, together we have some might, glinting in our damp holes at night. What are we?

Question: What goes up but never comes down?

Question: A wise person was once sentenced to death by a king. The king couldn't decide how to execute him so he said to the wise person, you can say anything you want, if it is true, I will hang you, if it is not true I will shoot you. In the end the king released the wise man. What did the wise man say?

Question: What can you hear but not see?