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

Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

Which alphabet letter is a question?

John said, "If yesterday was tomorrow, today would be Friday."

When did John make this statement?

Below the four parts have been reorganised. The four partitions are exactly the same in both arrangements. Why is there a hole?

A word I know,
Six letters contain,
Subtract just one,
And twelve is what remains.

Do You See It?

What has hands, but can’t clap?

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?

In the attached figure, you can see a chessboard and two rooks placed on the chess board. What you have to find is the number of squares that do not contain the rooks. How many are there?