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

Can you replace the question mark with the correct number?

A train full of passengers goes through a tunnel. When the train comes out from the other end, there is no single person on the train.

How did it happen?

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

Decode this picture on T-Shirt and tell what it says ?

What is the next number in the series?

15 29 56 108 208 ?

At my favorite fruit stand,
an orange costs 18,
a pineapple costs 27,
and a grape costs 15.
Using the same logic, can you tell how much a mango costs?

You find yourself in a strange place guarded by two guards.One of the guard always say truth while other always lies.You don't know the identity of the two.You can ask only one question to go out from there. What should you ask?

What occurs twice in a week, once in a year but never in a day?

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

Explain?