You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. 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?

I am white when I am dirty, and black when I am clean. What am I?

How many times can you subtract the number two from the number fifty?

Can you find the missing piece of the Porsche?

What have one eye but still cannot see?

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?

There are four 3-link chains. All you have to do is join them into a big 12-link chain. For joining two closed links, one of the links must be cut and placed onto the other link for closing.

How many minimum links will you have to cut to make the big chain?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?

What has to be broken before you can use it?