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?

A number can be multiplied by multiple of nine
i.e 9 18 27 36 45 ...

and the resulting number consist of only one digit.

Can you identify the number ?

Can you count the number of triangles in the given picture?

Decode below rebus
D
N
A
T
S , D

As easy as you can get into me, it is as hard to get out of me.

Do you know what I am?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

You see me once in June, twice in November, and not at all in May. What am I?

Using the clues below, what four numbers am I thinking of?

The sum of all the numbers is 31.
One number is odd.
The highest number minus the lowest number is 7.
If you subtract the middle two numbers, it equals two.
There are no duplicate numbers.

Can you make a fire with just a single stick?

Decode the below four famous ciphers:

8P of the SS
1M of the E
1S of the SS
60M in 1H