What is common among 11, 69, and 88?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

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

Explain?

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

P is the father of Q and S is the son of R. T is the brother of P and has a daughter U. If R is the sister of P, then what is the relation between U, Q and S?

A mother is 21 years older than her child. In exactly 6 years from now, the mother will be exactly 5 times as old as the child.
Where's the father?

If we add four times the age of John four years from now to five times his age five years from now we get ten times his current age.

How old will John be two years from now?

After a heavy Thanksgiving meal, the night watchman went to work. In the morning, he told his boss he had dreamed that a saboteur planted a bomb in the factory and that he felt it was a warning. The boss promptly fired him. Worker confused, Why boss fire him?

Why do you find that most of the buildings are deprived of the 13th floor?

A number can be multiplied by multiple of nine
i.e 9 18 27 36 45 ...

and the resulting number consist of only one digit.

Can you identify the number ?