I travel all around the world but always stay in the corner. What am I?

A train full of passengers goes through a tunnel. When the train comes out from the other end, there is no single person on the train.

How did it happen?

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

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.

Which is the smallest number that you can write using all the vowels exactly once?

John has played 50 ODI's and his average is 50. How many runs should he score in his 51st ODI, so that his average score jumps to 51?

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?

I have nine bottles of wine and one of the nine bottles is poisoned.
I need to find the poisoned bottle with two facts
(1) Poison is deadly, only a sip will cost death
(2) I have two mice to do so.

How should I do it?

Place the numbers from 1 to 9 in the circles in a manner that each side of the triangle sums up to 17.

Can you circle exactly four of these numbers such that the total is twelve?

1 6 1
6 1 6
1 6 1
6 1 6