What has many keys but can’t open a single lock?

A man had five children. He had $100 with him to give to his children. He decided to start with the youngest child and then give $2 more than each younger child to his next elder child.

For example, if he gives $x to the youngest child, he will give $(x+2) to the next one, $[(x+2) + 2] to the next one and so on.

Can you find out how much did the youngest one receive?

You enter your friend's room. He is not in his room. Although you see that on the bed there are two dogs, five cats, two giraffes and three pigs. Also, a couple of chickens and ducks are flying in the room.

Calculate the number of legs standing on the floor.

How can you make number one disappear by adding something to it?

The more of this there is, the less you see. What is it?

Where do fish keep their money?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

How can one talk without saying a single word?

Alpha is Beta's sister.

Gamma is a Beta mother.

Delta is Gamma's father.

Tango is Delta's mother.

Then,

How is Alpha related to Delta?

What is the longest word in the dictionary?