On a sheet of paper, write a number between 50 and 100.
Save this first number, you will use it twice.
Be careful ! Your number has to be over 50 and under 100.

 

As soon as you are ready,
click on

 

Add to this number.
Write your result on a sheet of paper.

 

And when you are ready
click on

 

Now using the sum you got, cross out the farthest digit to the left,
and add the digit you just crossed out to the remaining number.

Example : with a sum of 153, you get 53 then (53+1) =54

 

As soon as you are ready,
click on

 

Subtract the last number you got from
the first number you wrote on your paper.

As soon as you are ready,
click on

Let's have a look... You wrote , on your paper.