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?

When it is alive we sing, when it is dead we clap our hands. What is it?

Can you count the number of blocks in the picture below?

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

We have shown you a regular water barrel as below. Without using any measuring device can you check if the barrel is more than half-filled or less than half-filled?

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

In two decks of cards, what is the least amount of cards you must take to be *guaranteed* at least one four-of-a-kind?

You can hear me, but you can't touch or see me.

What am I?

There is a number which when you multiply by 3 and subtract 2 from the result, then the resulting number is the reverse of the actual number.

What is the smallest number that stands true on the statement?

What am I?