What is both possible and impossible at the same time?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

Replace the question mark with the number below given a simple math problem.

A clock loses 10 minutes each hour. If the clock is set correctly at noon, what time is it when it reads 3 PM?

Teacher ask the student

'Why are you standing on that chair in music class ?'.

what did student replied ?

I am weightless, but you can see me. Put me in a bucket, and I'll make it lighter. What am I?

John has eleven friends. He has a bowl containing eleven apples. Now He wants to divide the eleven apples among his friends, in such a way that an apple should remain in his bowl.
How can He do it?

A chess tournament is taking place on knock-out terms (the one who loses the match is out of the game).
(a) If 10 matches are played in total, how many players participated?
(b) If 20 players took part in the tournament, how many matches were played?

What does this rebus puzzle means ?

Which Travels Faster? Solve below famous picture riddle: