Ask your friend to write down any number of three figures in which the difference between the first and last figures is two or more than two. imagine he has written 317. Tell him to change the places of the first and the third figures
Then he must subtract the smaller number from the larger (713-317 = 3%). At last he must change the places of the figures in this answer and add them to the answer (693 + 396 = 1089).
"Now, if you breathe on the glass of that window," you say to him, "you will sec the answer on the glass." When he breathes on the glass, he will sec number 1089 on the window.
The secret is very simple: the answer is always 1089. Before you do the trick, put some detergent in a glass of water, then put your finger in the water and write with it 1089 on the window. Nobody can see the writing when it is dry, but when somebody breathes on the glass the place where your finger touched the glass will not become darker.
