Find a book, a pen, a piece of paper and a calculator.
Hand them to your friend.

Ask a friend to choose any page in the book.
Ask your friend to write down the page number on a piece of paper.
Example : In the video, we chose page 141

Now ask your friend to choose one of the first nine lines on that page.
Ask your friend to write down the line number that has been chosen.
Example : In the video, we chose line 7

Ask you friend to choose one of the first nine words on that line.
Ask your friend to write down the number of the word chosen.
Example : In the video, we chose word 3

Close the book

Hand your friend a calculator and ask your friend to follow these seven steps:

Multiply the page number by 2
Example from the video :  141 x 2 = 282

Multiply the answer by 5
 282 x 5 = 1410

Add 20
1410 + 20 = 1430

Add the line number
1430 + 7 = 1437

Add 5
1437 + 5 = 1442

Multiply the answer by 10
1442 x 10 = 14420

Add the word number
14420 + 3 = 14423

Now ask your  friendto tell you the answer.

You must now subtract 250 from that number.
  14423 - 250 = 14173

The last number (3) will tell you the number of the word  that your friend picked.

The second to last number (7) will indicate the line number

The remaining numbers (141) will indicate the page number.

Take the book, turn to that page, find line and word on that line.

Magic!