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?

Why do we preferably have round manhole covers and not square ones?

You are given a cube that is made with the help of 10x10x10 smaller cubes summing up to a total of 1000 smaller cubes. You are asked to take off one layer of the cubes.
How many remain now?

Two fathers and two sons went fishing one day. They were there the whole day and only caught 3 fish. One father said, that is enough for all of us, we will have one each. How can this be possible?

Can you make four (4) nines (9) equal 100?

In a stable, there are men and horses. In all, there are 22 heads and 72 feet. How many men and how many horses are in the stable

What number comes next in this sequence:
7 8 5 5 3 4 4 _

In the picture, you can see a chess board. On the top left position, the K marks a knight. Now, can you move the knight in a manner that after 63 moves, the knight has been placed at all the squares exactly once excluding the starting square?

Can you write down eight eights so that they add up to one thousand?

What is the Surname of Barbie Doll?