I shave every day, but my beard stays the same. What am I?

What is the centre of gravity?

In which direction should the missing arrow point?

what's the probability of getting a king or a queen from a pack of 52 cards?

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

You are in a room with no metal objects except for two iron rods. Only one of them is a magnet.
How can you identify which one is a magnet?

It's a test that will check your IQ.

Suppose you have one 11 minute hourglass and one 13 minute hourglass.

Can you measure exactly fifteen minutes using them ?

Which statement is true out of the following?
One statement here is false.
Two statements here are false.
Three statements here are false.

Place a mathematical symbol between the numerals 5 and 9 in such a way that the resulting number is greater than 5 but smaller than 9.

When Jack was six years old he hammered a nail into his favourite tree to mark his height. Ten years later at age sixteen, Jack returned to see how much higher the nail was. If the tree grew by five centimetres each year, how much higher would the nail be?