If eleven plus two equals one, what does nine plus five equal?

A boy was at a carnival and went to a booth where a man said to the boy, "If I write your exact weight on this piece of paper then you have to give me $50, but if I cannot, I will pay you $50." The boy looked around and saw no scale so he agrees, thinking no matter what the carny writes he'll just say he weighs more or less. In the end the boy ended up paying the man $50. How did the man win the bet?

I live in a bowl. I can swim. I have a tail. I also have fins and big eyes. What am I?

What is black when you buy it, red when you use it, and gray when you throw it away?

The answer I give is yes, but what I mean is no. What was the question?

What runs around the whole yard without moving?

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

Its something that each of us devours,
Not just us but birds, beats, trees, and flowers,
Frets iron and nibbles steel,
Toil hard stones to meal,
Exterminates king, collapse town,
And blows the mountains down.

I cannot talk, but I always reply when spoken to. What am I?

Can you find out which number multiplied by itself will give the output as 12345678987654321?