What is more useful when it is broken?

Replace each alphabet with the number (1-9) to make the below equation correct.

AB * C = DE - F = GH / I

There was a man he lives in a hotel each morning he presses the first floor button each evening if there is a person in the elevator he asks him to press the 10 floor button if there is no one in the elevator he takes the stairs why.

What does this rebus means ?

Why Wine Glass Stem is so long?

How many sides does a circle have?

John is found dead in a bare field. Nobody killed John,
John did not commit suicide.

Inspector Jacob found a bag just a few meters away from John which could save his life. What was in the bag?

The dirtier I get, the whiter I look. Who am I?

I am the one who remains awake when you sleep. But I need to rest when you awake. Who Am I?

It's a protector.
It sits on a bridge.
One individual can see directly through it, while others wonder what it hides.

What is it?