When my father was 31 I was 8. Now he is twice as old as me. How old am I?

Can you find out what is missing?

1 3 5
2 4 ?

Hint: It's not six. Think out of the box.

Considering the below equation:

V + II - VI = 10
IV - X + VIII = 20
IV - VII + VI = 30

Then, I + II + III = ?

Once while in his court, King Akbar asked Birbal to write something on a wall that makes one sad when read in good times and makes one happy when read in sad times.

He took only a few moment and wrote something that fit the requirements. What did he write?

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?

You can hear me, but you can't touch or see me.

What am I?

I always drive my customer away.

Who am I?

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

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

Can you find out the next digit in the following series ?

0, 0, 1, 3, 2, 6, 3, 9, 4, 12, 5, ?