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

A girl was sitting in her hotel room when she heard a knock on the door. She opened the door and found that a man was standing outside.
The man said, "Oh! I am really sorry, I thought this was my room."
He then walked through the corridor to the elevator. The girl did not know the man. She closed her door and called security asking them to apprehend the man.
What made her suspicious of that man? He might have been genuinely mistaken.

Speaking of rivers, a man calls his dog from the opposite side of the river. The dog crosses the river without getting wet, and without using a bridge or boat. How?

Why is the Hole below a Lock?

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?

How can you throw a ball as hard as you can and have it come back to you even if it doesn't hit anything there is nothing attached to it and no one else catches or throws it.

What is the last thing you take off before bed?

1. Where does Easter come from before Valentine's Day?

2. Do you know what is in the middle of Valentine's?

3. What did the lady bee say to the man bee on the occasion of Valentine's Day

Do you know who was buried in John's tomb?

It has horns but can’t beep. It is like to bleat but It is not a sheep. What is it?