Funny Riddles

Question: What is a word made up of 4 letters, yet is also made up of 3. Sometimes is written with 9 letters, and then with 4. Rarely consists of 6, and never is written with 5.

Question: What grows up and down at the same time?

Question: What is bought by the yard by is worn by the foot?

Question: It smells like blue paint,
pours like green paint,
and it looks like a red truck.

What is it?

Question: I have all of your knowledge but could fit in your hands.

What am I?