What is the Surname of Barbie Doll?

Once while in his court, King Akbar asked Birbal to write something on a wall that makes one sad when read in good times and makes one happy when read in sad times.

He took only a few moment and wrote something that fit the requirements. What did he write?

Why do you find that most of the buildings are deprived of the 13th floor?

There is a square piece of paper with a hole that is denoted by the circle on the top right side in the given picture. You have to cut the paper in a manner that it forms two and only two separate pieces of paper and then rearrange the pieces in a manner that the holes come in the centre of the paper.

Can it be possible to build a house that has all its four walls facing towards the South?

What does it mean?

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

What can run but never walks, has a mouth but never talks, has a head but never weeps, has a bed but never sleeps?

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

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?