When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

In an interview, a boy was asked an unusual question 'How two persons sitting with a table in between them can't see each other?' He was unable to reply. Can you?

Without looking at a calendar, within a minute name, a boy's name using 5 consecutive 1st letters of 5 consecutive months

I have a hole in my back and legs I lack.
I live where I can’t breathe and I eat without teeth.
What am I?

What have one eye but still cannot see?

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

I am weightless, but you can see me. Put me in a bucket, and I'll make it lighter. What am I?

If an electric train is travelling south, then which way is the smoke going?

How can you write nineteen in a manner that if we take out one, it becomes twenty?

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