Name a key which is hardest to turn.

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?

There was an aeroplane crash, every single person died, but two people survived. How is this possible?

When is the top of a mountain similar to a savings account?

Why are televisions attracted to people?

A network of 20 x 10 squares is given to you.

Can you calculate how many unique squares and rectangles can be formed combining two or more individual squares ?

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

I don't get anymore wetter, no matter how much rain falls on me.

Find The Next Number in this series.
1, 2, 6, 42, 1806 ?

What is the end of everything?