Can you replace the question mark with the correct number?

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

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

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 ?

What can run but never walks, has a mouth but never talks, has a head but never weeps, has a bed but never sleeps?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?

How many times can you subtract the number two from the number fifty?

The picture shows the dice results in each couple of throws. If they are actually following a pattern, can you find out the missing one?

John went to meet his friend Jacob, but when he was about to reach the main gate, John notices that Jacob had a mighty dog who was fastened to the tree. The chain is long enough that it allows the dog to reach the main gate.

How can the John reach the main gate?

Which is heavier: a ton of bricks or a ton of feathers?