What goes up but never comes down?

Why do you find that most of the buildings are deprived of the 13th floor?

A father's child, a mother's child, yet no one's son.

Who am I?

If you drop me I’m sure to crack, but give me a smile and I’ll always smile back. What am I?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

By what process could you make a 'Tea-Table' into food?

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.

The first box has two white balls. The second box has two black balls. The third box has a white and a black ball.

Boxes are labeled but all labels are wrong!

You are allowed to open one box, pick one ball at random, see its colour and put it back into the box, without seeing the colour of the other ball.

How many such operations are necessary to correctly label the boxes?

There once were seven dwarfs who were all brothers. They were all born two years apart. The youngest dwarf is seven years old. How old is his oldest brother?

I am a word that begins with the letter “i.” If you add the letter “a” to me, I become a new word with a different meaning, but that sounds exactly the same. What word am I?