By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?

You have two buckets of 11 liters and 6 litres.
How can you measure exactly 8 litres?

Take away my first letter, then take away my second letter. Then take away the rest of my letters, yet I remain the same. What am I?

I am quite hot but become too cold if you remove the first two letters. What am I?

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?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

Outside a tattoo artist's shop, there was a signboard which read 'I make tattoos on only them who do not tattoo themselves'.

Reading it what do you think, does the tattoo artist tattoo himself?

Prove that twice of ten is the same as twice of eleven.

I’m tall when I’m young, and I’m short when I’m old. What am I?

What is the riddle which can be asked all day with a different correct answer each time.