If eleven plus two equals one, what does nine plus five equal?

You throw me out when you want to use me and you take me in when you don't want to use me.

Who Am I?

O_er_t_o_

Complete the missing letters of the given word.

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

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

I have four wings but can't fly.
I express no emotions.
I am found on the exact spot every time you look.
I keep toiling away with a little sound.

Do you know what am I?

The more you take me, the more you leave me behind.
Who Am I?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

Twice ten are six of us,

Six are but three of us,

Nine are but four of us;

What can we possibly be?

Would you know more of us?

Twelve are but six of us,

Five are but four, do you see?

What are we?

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