Can you convert the number zero(0) into a positive number using just one mathematical operator ?

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?

How many words can a quill made with the feather of a pigeon write with a 100ml bottle of black ink?

In 1990, a person is 15 years old. In 1995, that same person is 10 years old. How can this be?

There are forty elephants and they have forty-fore heads. How can this be possible?

A doctor and a boy were fishing. The boy was the doctor’s son, but the doctor was not the boy’s father. Who was the doctor?

Solve the mathematical equation in the picture below.

I get hot but I never sweat,
I cook food but I am not a chef,
I have a door but you can't enter me,
I have a light but I am not a lamp.
Who am I?

A man is found hanging dead from the ceiling of a room. The room’s dimensions are 15 x 15 x 15. The man is only 6ft tall and the rope was only 2ft long. There are no windows and only one door to the room. The door is bolted shut from the inside, and a puddle of water is under the man. How did he kill himself?

Until it is measured, not known. Yet how you miss it when it has gone. What is it?