4.8.4 Here’s the Trick!

Now for the party trick! Create a large 5×5 grid. Write down the number 65 on a piece of paper and fold it up so that the number is not visible. Announce that you are going to predict the sum of the five numbers your friend chooses from the grid. Ask the friend to choose the numbers following the rules given above and also to work out the sum.

[ It is not a good idea to repeat this puzzle with the same audience—otherwise your trick may be discovered. However, you can extend these grids or even invent some new puzzles of your own! ]

Assuming no mistakes have been made, you can then dazzle your audience by producing the piece of paper with exactly the same sum written on it—ensuring your party is a success instead of a snooze!

4.8.3 Understanding the Puzzle

4.8.5 Human Calculator