How many sides does a circle have?

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

I possess a head

I flaunt a tail

But I don't have mouth or legs

Can you find out who I am?

I am beautiful, up in the sky. I am magical, yet I cannot fly. To people I bring luck, and to some people, riches. The boy at my end does whatever he wishes. What am I?

John enters a small room. The Door Closes.
When the door opens, John is in a larger room.

Explain?

It is an eleven letter word.
The first, second, third and fourth letters form a banquet's name.
The fifth, sixth and seventh letters form a car's name.
The eighth, ninth, tenth and eleventh letters form a mode of transport.

Can you identify what word it is?

I’m light as a feather, yet the strongest person can’t hold me for five minutes. What am I?

The Puzzle: A girl, a boy, and a dog start walking down a road.

They start at the same time, from the same point, in the same direction.

The boy walks at 5 km/h, the girl at 6 km/h.

The dog runs from boy to girl and back again with a constant speed of 10 km/h. The dog does not slow down on the turn.
How far does the dog travel in 1 hour?

There are a number of books on a shelf. If one book is the 4th from the left and 6th from the right, how many books are on the shelf?

The dirtier I get, the whiter I look. Who am I?