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

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

I am under you when I am whole.
I shift above you if you remove the first letter.
I come all around you if you remove the second as well.

Can you tell me who I am?

John was piloting a plane behind a car but was never able to overtake it. Why?

John’s parents have three sons: Snap, Crackle, and what’s the name of the third son?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

Can you find the missing piece of the Porsche?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

O_er_t_o_

Complete the missing letters of the given word.

What can run but never walk, have a mouth that never speaks, have a head that never weeps, and have a bed but never sleeps?