How many sides does a circle have?

One day, John and his friends were playing around. Jacob hit something with a Pin and it popped. John's dad came into the room that very moment, but he wasn't mad. In fact, he was smiling. What did Jacob hit?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

Can you find the missing piece of the Porsche?

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.

There are four 3-link chains. All you have to do is join them into a big 12-link chain. For joining two closed links, one of the links must be cut and placed onto the other link for closing.

How many minimum links will you have to cut to make the big chain?

A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

Can you spot what's wrong with the following sentence?

PETER WAS ANGRY AT
HIMSELF BECAUSE HE
ACCIDENTALLY LEFT THE
THE KEYS TO HIS CAR
AT HIS FRIEND'S HOUSE.

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

When I go in I might cause pain. I cause you to spit and ask you not to swallow. I can fill your hole. What am I?