Why do people go to bed?

In the picture given below, can you find out which digit will take place of the question mark?

100 prisoners are stuck in the prison in solitary cells. The warden of the prison got bored one day and offered them a challenge. He will put one prisoner per day, selected at random (a prisoner can be selected more than once), into a special room with a light bulb and a switch which controls the bulb. No other prisoners can see or control the light bulb. The prisoner in the special room can either turn on the bulb, turn off the bulb or do nothing. On any day, the prisoners can stop this process and say "Every prisoner has been in the special room at least once". If that happens to be true, all the prisoners will be set free. If it is false, then all the prisoners will be executed. The prisoners are given some time to discuss and figure out a solution. How do they ensure they all go free?

What number do you get when you multiply all of the numbers on a telephone's number pad?

There are are five things wrong with this sentence; only geniuses will be able to to spot all of the mitstakes

Three people are in a room. Ronni looks at the Nile. The Nile looks at Senthil. Ronni is married but Senthil is not married. At any point, is a married person looking at an unmarried person? Yes, No or Cannot be determined.

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

Teacher ask the student

'Why are you standing on that chair in music class ?'.

what did student replied ?

What 5-letter word typed in all capital letters can be read the same upside down?

If you're 8 feet away from a door and with each move you advance half the distance to the door. How many moves will it take to reach the door?