What's the only room from which no one can enter or leave

Here is a mathematical expression that also secretly tells a movie name. What movie is that?

How can you write nineteen in a manner that if we take out one, it becomes twenty?

Why is 6 afraid of 7?

Can you name an animal whose killing cannot be performed without spilling your own blood?

One absent-minded ancient philosopher forgot to wind up his only clock in the house. He had no radio, TV, telephone, internet, or any other means for telling time. So he travelled on foot to his friend's place a few miles down the straight desert road. He stayed at his friend's house for the night and when he came back home, he knew how to set his clock. How did he know?

It has five wheels, though often think four, You cannot use it without that one more, You can put things in it, you can strap things on top, You can't find it in the market, but you can still go shop. What is it?

What is the largest number you can write with just 3 digits?

An octopus has 8 legs. A hippogriff has 6 legs and 2 pairs of wings. A sphinx has 6 legs and one pair of wings. Now we have all 3 kinds and a total of 18 insects in a cage. We have a total of 118 legs and 20 pairs of wings. How many insects do we have of each kind?

What breaks yet never falls, and what falls yet never breaks?