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

It can't be seen, can't be felt, can't be heard, and can't be smelt.
It lies behind stars and under hills, And empty holes it fills.
It comes first and follows after, Ends life, and kills laughter.
What is it?

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

Can you move 2 matchsticks to form four equal sized squares.

What has 88 keys?

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

What does below pictogram mean?

Can you find the ages of a son, father and grandfather based on the following facts?
The sum of the ages of grandfather, father and son is 140 years.
The age of the son in months is the same as the grandfather in years.
The age of the son in days is the same as the father in weeks.

What is the centre of gravity?

What number do you get when you multiply all of the numbers on a telephone's number pad?