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?

I have lakes with no water, mountains with no stone and cities with no buildings. What am I?

Solve this riddle by finding the odd one out from the rest.

When monkey rotate the gear, which mark will be hit 1 or 2 ?

If you drop me I’m sure to crack, but give me a smile and I’ll always smile back. What am I?

A finger goes in me. You fiddle with me when you're bored. The best man always has me first. What am I?

John was piloting a plane behind a car but was never able to overtake it. Why?

Can you count the number of seconds in a year?

Clue: You need to bother about calculation.

what does the below rebus mean?

What does this mathematical rebus means ?