What occurs twice in a week, once in a year but never in a day?

John left on a horse on Thursday , was gone for two days, and came back on Thursday after completing his work. How did that happen?

What's a single-digit number with no value?

You are presented with three boxes. One of them has a red ball inside and the other two have a black ball inside each of them. You are asked to pick up the one with red ball and you pick one. Now, one of the other boxes is opened and it is found to have a black ball.

You are presented with a chance to change your box with the one that is left closed. Will you change your box? Why or why not?

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?

Can it be possible to build a house that has all its four walls facing towards the South?

What does this mathematical rebus means ?

What can you hold in your right hand, but never in your left hand?

There is a place where if I stand up straight, I will still be considered sideways.

A man was found murdered on Sunday morning. His wife immediately called the police. The police questioned the wife and staff and got these alibis: The Wife said she was sleeping. The Cook was cooking breakfast. The Gardener was picking vegetables. The Maid was getting the mail. The Butler was cleaning the closet. The police instantly arrested the murderer. Who did it and how did they know?