I am looking for a word that change both gender and number when i add the letter 'S'.

What Word am I Looking For ?

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

which number am I?

4 fathers, 2 grand-fathers and 4 sons went to watch the movie.What is the minimum number of tickets they need to buy ?

A mother is 21 years older than her child. In exactly 6 years from now, the mother will be exactly 5 times as old as the child.
Where's the father?

A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

You have an empty wine bottle with a cork that has been secured at the top in a normal way. There is a metal ring inside the bottle that is suspended by a string.

How can you make the metal ring drop to the bottom if you are not allowed to touch anything - not the bottle, not the cork, not the thread and not the ring?

They do not possess flesh or feathers or scales or bone
But still, they are blessed with fingers and thumbs of their own.

The person who makes it has no need for it; the person who buys it has no use for it. The person who uses it can neither see nor feel it. What is it?

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see?

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

Who am I?