Replace the question mark with the correct number in the below-given picture?

Why is the Hole below a Lock?

How can you make number one disappear by adding something to it?

If one and a half boys, eat one and a half burgers in one and a half hours.

How many burgers can 9 boys eat in 3 hours?

Can you name any English verb that becomes its past tense by simply rearranging the alphabets ?

How can you drop a raw egg from a height onto a concrete floor without cracking it?

A man was gazing through the window of the 23rd floor of the building. He suddenly opened the window and jumped on the other side of the window. On landing on the floor, there was not a sheer mark of injury on him.

How can that be possible if he did not use any kind of parachute and did not land on a soft surface?

I cry without having a voice.
I fly without having wings.
I bite without having teeth.
I whisper without a mouth.

Who am I?

What's the only room from which no one can enter or leave

Forwards I am heavy, backward I am not. What am I?