The effect: The spectator is merely thinking of a number between 22 and 99. You draw a 4×4 magic square and show it to the spectator. The spectator is unimpressed. You reveal to the spectator that the sum of the numbers in row 1 is their secret number. In fact, the sum of the numbers in row 2 is their number, same with row 3 and 4. The same for each column, the same for the diagonals, indeed there are 28 unique combinations on your magic square that reveal their secret number.
The method- The secret Number: There are several ways to present this effect. One method involves asking the spectator to name any number between 22 and 99. You then draw the magic square and appear like a maths whiz. There exist other methods to present the effect in which the spectator doesn’t name a number and from their perspective, they are thinking of a freely selected number that you are supposedly not aware of however gimmicks are normally required for this ends. Another method involves forcing a number on the spectator. This can be achieved by forcing the top two cards from a deck of cards onto the spectator eg using a riffle force or the very simple cross-cut force that requires no skill and can be learnt here: https://www.youtube.com/watch?v=Tkte5Ubo9yc.
The method- The magic square: Regardless of what number the spectator chooses between 22 and 99, there will be 12 of the 16 squares in the magic square that will be the same every time. The remaining 4 squares will depend on the number the spectator has chosen. Fortunately, there is an easy method to remember the numbering of the squares.
1.Firstly, write out the multiples of 18. This covers: 18, 36, 54, 72. Make sure only one digit appears in each square and the numbers are vertical. The location of these digits appears below.
2. Write out the numbers 9, 10, 11, 12. The number 9 appears in the bottom right corner and the numbers increase by 1 along the zig-zag. See the below image.
3. There will be 4 spaces remaining. You must now fill in square ‘A’. A is the spectators number minus 21. Move anti-clockwise around the blank squares and add 1 each time. See the below image.
An example of a completed magic square appears below. This magic square was drawn with the number 46 being chosen as the spectator’s number.
Puzzle a Day 