Amazing Fido "online telepathy" puzzle

Someone sent me a link to an "online telepathy" puzzle, I find it very interesting. Give it a try yourself to see if you agree and then try to figure out how it was done.

First, click on the link below. It should open up a new window to the puzzle website. Click on the boy in the lower right corner of the picture to start the puzzle. Simply follow the instruction on screen.

When you have reach the final window, type in your answer in the white box using the keyboard and then watch what happen to the paper in the boy's hand. You will be amazed.

To try it, click on the link here Fido Puzzle

To find out the answer, read on ....

The Answer ...

After you have decided on the 3 or 4 digits, jumble them up, the answer you get, be it 3 digits or 4 digits answer, will always adds up to 18.

Example, if after the subtraction, you get 3672 ... 3+6+7+2 = 18.

Let take a couple of random examples:

Example 1.
You chose 5476 .... jumble it up to become 6457
Bigger number subtract smaller number .... 6457 - 5476
That will give you 981
9+8+1 = 18

Example 2.
You chose 9876 .... jumble it up to become 8967
Bigger number subtract smaller number .... 9876 - 8967
That will give you 909
9+0+9 = 18

Now, with the remaining 3 digits that you type into the box after you have circled one of them, all we have to do is use 18 to subtract them one by one.

In the case of the first example 3672, if you had choosen 7, then 18-3-6-2 will give you the answer 7, which is the one you had circled.

Important: The initial instruction to chose the 3 or 4 digits have to be a set of random numbers all different from each other.