Which number should replace the question mark?

No matter how little or how much you use me, you change me every month. What am I?

A mules travels the same distance daily.
I noticed that two of his legs travels 10km and the remaining two travels 12km.
Obviously two mules legs cannot be a 2km ahead of the other 2.

The mules is perfectly normal. So how come this be true ?

Can you find the missing piece of the Porsche?

An ape is trying to climb on a pole that is 60 feet high. Due to the slippery surface, the ape climbs 3 feet in a minute only to slip back 2 feet.

How much time do you think the monkey will take to reach the top of the pole?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

It is deaf, Dumb and Blind!!!

Still, always tells the truth. What is it?

A guard is positioned at the one side of the bridge saying ‘A’. His task is to shoot all those who try to leave from ‘A’ to the other side and say ‘B’. He also need to welcome the person who comes from another side ‘B’ to his side ‘A’. The guard comes out of his post every 1 hour and looks down the bridge for any people trying to leave. You are at side ‘A’ and wish to go to another side ‘B’. you also know that it would take 1:45 hr to cross the bridge. How will you cross the bridge?

The peacock is a bird that does not lay eggs. How do they get baby peacocks?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?